Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

Contents lists available at ScienceDirect

Palaeogeography, Palaeoclimatology, Palaeoecology

j ourna l homepage: www.e lsev ie r .com/ locate /pa laeo

Anchovy population and ocean-climatic fluctuations in the HumboldtCurrent System during the last 700 years and their implications

Marcos Guiñez a,b,c,⁎, Jorge Valdés b,c, Abdel Sifeddine c,d,e, Mohammed Boussafir f, Paola M. Dávila g,c

a Doctorado en Ciencias Aplicadas, Mención Sistemas Marinos Costeros, Universidad de Antofagasta, Chileb Laboratorio de Sedimentología y Paleoambientes, Instituto de Ciencias Naturales Alexander von Humboldt, Facultad de Ciencias del Mar y Recursos Biológicos, Universidad de Antofagasta,casilla 170, Antofagasta, Chilec Laboratorio Mixto Internacional, PALEOTRACES (Institut de Recherche pour le Developpement, Universidade Federal Fluminense, Universidad de Antofagasta), Chiled LOCEAN, UMR 7159 CNRS-IRD-Univ. P. and M. Curie-MNHN, 32 Av. Henri Varagnat, 93143 Bondy, Francee Departamento de Geoquímica, Universidade Federal Fluminense, Niteroi, RJ, Brasilf Université d'Orléans, Université François Rabelais - Tours, CNRS/INSU; Institut des Sciences de la Terre d'Orléans - UMR 6113, Campus Géosciences, 1A, rue de la Férollerie,45071 Orléans cedex 2, Franceg Departamento de Ciencias Acuáticas y Ambientales, Facultad de Ciencias del Mar y Recursos Biológicos, Universidad de Antofagasta, casilla 170, Antofagasta, Chile

⁎ Corresponding author.E-mail address: marcos.guinez@uantof.cl (M. Guiñez)

http://dx.doi.org/10.1016/j.palaeo.2014.08.0260031-0182/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 25 July 2013Received in revised form 21 August 2014Accepted 26 August 2014Available online 6 September 2014

Keywords:Sedimentary recordOcean-climatic conditionsAnchovy populationGleissberg solar cycle

Amarine sedimentary record collected from87mwater depth in a coastal environment of theHumboldt CurrentSystem (Mejillones Bay, 23° S, northern Chile) was used to reconstruct the past 700 years of ocean-climatic con-ditions and to study the influence of any changes on anchovy population dynamics.We analyzed quartz, organiccarbon, total nitrogen, alkenones andfish scales. Four stratigraphic units in the sediment columncorrespondwithfluctuations in these and other proxies. Low Scale Deposition Rate (SDR) values from 1330 to 1420 suggest a lowabundance of anchovy in this coastal environment. Three subsequent cycles of ca. 170 years each showed anincrease and decrease of anchovy populations, which is in agreement with changes in the wind regime, seasurface temperature and primary productivity.Since ca. 1840, marked fluctuations of SDR have been observed, probably as a consequence of the onset of adifferent oceanographic regime characterized by intensified southern winds and upwelling, colder surfacewaters, higher primary productivity, and enhanced “La Niña like” interdecadal variability. An increase of theanchovy population was observed until halfway through the 20th century, followed by a decrease, even thoughwater temperature decreased and primary productivity increased. This situation is likely the consequence of theincreasedfishery activity that developed in this zone during the last 60 years. After analyzing the results obtainedfor anchovy SDR, we can determine that there is a relation between the abundance of this species and phases ofthe Pacific Decadal Oscillation (PDO), in which an increase in the SDR coincides with a PDO cold phase, while adecline coincides with a warm phase.Fast Fourier transformation analysis applied to the time series obtained from theMejillones sediment core and tothe North Atlantic Oscillation (NAO), the PDO, and the solar irradiance index time series shows three differentdecadal cycles (80–100 years, 61–75 years and 45–48 years approximately). Furthermore, the results of thisstudy suggest that both the PDO and the NAO and the biogeochemical markers of Mejillones exhibit periodicitiesthat fall within the 80 to 100 year Gleissberg solar cycle, indicating that global solar radiation plays a key role inthe local ocean-climatic processes and confirming teleconnection linkages between widely separated regions.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Coastal upwelling systems provide the largest net production inrelation to ocean yields around the world. The most importantupwelling areas are found in South America (Chile–Perú), NorthAmerica (California) and Africa (Namibia and Mauritania) (Escribanoand Morales, 2004). The Chile–Perú current system is one of the most

.

productive oceanic areas (4 to 20 g C m−2d−1) (Daneri et al., 2000)due to the combined action of coastal upwelling and horizontal tidaltransport of nutrients by the Humboldt Current from the subantarcticregion (Bernal et al., 1983). Moreover, the upwelling centers have akey role in the development of biogeochemical and biological cyclesbecause primary productivity controls the preservation processes of or-ganic carbon in the ocean (Langue et al., 1990). Waters in these systemsare characterized by their low temperatures, low dissolved-oxygen con-tent and high concentrations of nutrients, thus resulting in a high primaryproductivity (Strub et al., 1998). A persistent characteristic within the

Fig. 1. Study area: the dot shows the sector from where the sediment core was collected. Water depths shown in meters.

Table 2Values obtained for the 14C dating.

Depth mg C δ13C Isotope fractionation Radiocarbon Age

211M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

main upwelling systems is the existence of an Oxygen Minimum Zone(OMZ), which, in the Humboldt case, extends from the south of Perú tothe center of Chile (Fuenzalida et al., 2009).

Coastal upwelling systems have different variability scales withrespect to their physicochemical and biological components. Seasonal,decadal and interdecadal variations have been described by differentauthors (Steele, 1998; Polovina, 2004; Overland et al., 2006; Takasukaet al., 2008) who connect this variability to ocean-climatic fluctuations.The fluctuations are small in scale if their occurrences are seasonal(warm and cold periods), but the ocean-climatic fluctuations can alsobe at annual and interdecadal scales like ENSO and the Pacific DecadalOscillation (PDO) (Chávez et al., 2003; Vargas et al., 2007). In addition,climate changes can occur at centennial and millennial scales, such asthe Medieval Climatic Anomaly (950–1350 AD), and the Little Ice Age(1500–1850 AD) (Gayo et al., 2012), which had major impacts on theupwelling systems (Sifeddine et al., 2008; Gutiérrez et al., 2009).

From a bioeconomical perspective (natural resources), the upwell-ing systems support most of the fishing activities in the ocean(González et al., 1998; Iriarte et al., 2000). In ecological terms, these sys-tems have a lowbiological diversity but a large biomass of pelagic fishes,

Table 1Values obtained for the 210Pb dating.

Depth(cm)

210Pb 210Pbexc

0.5 796 ± 23 751 ± 231.5 603 ± 18 567 ± 184 293 ± 9 234 ± 95 217 ± 17 157 ± 175.5 213 ± 15 150 ± 158 161 ± 7 76 ± 711 62 ± 9 18 ± 914.5 120 ± 15 46 ± 1518 103 ± 16 4 ± 1621.5 100 ± 14 24 ± 14

such as the anchovy (Engraulis ringens), the sardine (Sardinops sagax),and the horse mackerel (Trachurus symmetricus murphyi).

The sardine and the anchovy are small pelagic fish resources havinggreat commercial significance in northern Chile. The sardine rangesfrom the equator (01° 39′ S) to Chile (37°S), including the areas sur-rounding the Galápagos Islands, whereas the anchovy is found fromnorthern Perú to the south of Chile (Serra, 1983). In the northern areathese two species live in coastal regionswhere the biological productiv-ity is high due to frequent upwelling events throughout the year thatincrease during the summer (Escribano and Morales, 2004). These spe-cies represent around 20–25% of the world's annual fish catch (Alheitand Bernal, 1993; Hunter and Alheit, 1995).

From a paleoceanographic perspective, the relation between fishremains found on sediments and past fluctuations in the pelagic fishpopulations has been extensively examined in studies about the currentsystems of California, Perú and northern Chile (Soutar, 1967; Fitch,

(cm) (BP)

11 0.57 −19.2 90.25 ± 0.24 825 ± 3012 1 −19.2 89.8 ± 0.23 865 ± 3014.5 1.07 −19.9 90.03 ± 0.22 845 ± 3018 0.65 −19.7 89.79 ± 0.23 865 ± 3021.5 1.1 −18.9 89.14 ± 0.22 925 ± 3025.5 1.4 −20.2 89.38 ± 0.23 900 ± 3027 1.56 −18.4 88.6 ± 0.22 970 ± 3034 1.2 −19.1 88.76 ± 0.23 960 ± 3035.5 1.3 −21.4 89.02 ± 0.22 935 ± 3038,5 1.2 −20 87.79 ± 0.23 1045 ± 3040 1.5 −21.5 88.04 ± 0.24 1025 ± 3042 1.5 −19.9 87.3 ± 0.21 1090 ± 3043.5 1.2 −21.2 87.62 ± 0.21 1060 ± 3045 1.3 −19.8 86.48 ± 0.21 1165 ± 3046 1.2 −21 86.81 ± 0.23 1135 ± 3047 1.3 −25.4 87.54 ± 0.24 1070 ± 3053.5 1.2 −19.7 87.65 ± 0.22 1060 ± 3054 1.1 −19.5 87.72 ± 0.23 1055 ± 30

212 M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

1969; Soutar and Isaacs, 1969; Baumgartner et al., 1992; Tunnicliffeet al., 2001; Helly and Levin, 2004; Milessi et al., 2005; Valdés et al.,2008; Gutiérrez et al., 2009; Finney et al., 2010; Salvatteci et al., 2014).It is important to acknowledge the fact that fish in general and theanchovy in particular are subject to ocean temperature variations thatcan cause oscillations in their abundance (Aliaga et al., 2001; Chávezet al., 2003).

Mejillones Bay (23°S) is located offshore of the planet's driest desert(Atacama) seashore, and its mouth is oriented to the north. This bay ispart of the main upwelling center of Punta Angamos, which is locatedin the Northern Humboldt Current System (Marín et al., 1993). Severalstudies carried out in this bay (Rodríguez et al., 1986; Marín andOlivares, 1999, Marín et al., 2003) have documented that it has a highrate of primary productivity that can reach 138 mg C m−3 h−1 and arich phytoplankton diversity. The physico-chemical properties of the

0 5 10 15 20 25

210 P

bxs

(Bq/

Kg)

0

100

200

300

400

500

600

700

800 a)

0 10 20 30 40 50 60

Age

14C

(A

.D)

700

800

900

1000

1100

1200

1300 b)

0 5 10 15 20 25 30 35 40 45 50

Age

(A

.D)

1400

1500

1600

1700

1800

1900

2000

2100210 Pb14 C

R2 = 0,9982 c)

Deep (cm)

Deep (cm)

Deep (cm)

Fig. 2. (a) Activitymeasurements of from excess 210Pb present in the sedimentary column,(b) non-calibrated 14C ages, (c) age-depth plot from 210Pb and calendar-adjusted 14C datesby means of a linear regression.

water column (temperature, salinity and dissolved-oxygen content)show seasonal variations between the cold period (autumn–winter)and the warm period (spring–summer) (Avaria and Muñoz, 1982;Rodríguez and Escribano, 1996). At the same time, the upwelling fila-ments produced inMejillones Bay strongly influence the coastal ecosys-tem dynamics as they represent themain source of nutrient enrichmentof the water column surface. Moreover, the upwelling shadow insidethe bay represents a significant physical structure that affects primaryproductivity and promotes the larval retention (Castilla et al., 2002;Marín et al., 2003).

One of themain characteristics of Mejillones Bay is that it is stronglyinfluenced by theOMZ,which extends from60 to 500mwater depth offthe Mejillones coast (Silva and Sievers, 1981; Silva, 1983). Thedissolved-oxygen values recorded within the bay are under 1 ml L−1,below 50 m water depth (Navea and Miranda, 1980; Escribano, 1998),whereas between 60 and 80 m below sea surface, these values can beas low as 0.1 ml L−1, depending on the season (Valdés, 2004). Because

Fig. 3. Stratigraphic and chronological units of the sedimentary column.

Fig. 4. Comparison of the six paleoceanographic proxies used in this study. Horizontal dotted lines show different sedimentary phases, vertical dotted lines show the averages and theroman numerals indicate each sedimentary unit. OI is oxygen index and SDR is scale deposition rate for anchovy scales.

213M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

themaximumwater depth in the bay is 110m, the bottomenvironmentis largely under the OMZ influence. Several authors (Ortlieb et al., 2000;Valdés et al., 2009; Guiñez et al., 2010) highlight this bay as a potentialspecial environment for paleoenvironmental reconstructions due to theeffect exerted by the OMZ on sediments, thereby allowing the preserva-tion of biogenic remains (scales, foraminifers, diatoms and particulateorganic matter) and inorganic elements (metals and minerals). Morespecifically, the organic material preserved in Mejillones Bay is ofmarine origin, although it presents changes in its structural compositionassociated with degradation during transport in the water column(Valdés et al., 2000, 2004). Studies suggest that the bay's accrued sedi-ments clearly show evidence of the prevalence of suboxic/anoxic condi-tions in the depositional environment, particularly during the lastmillennium. Research carried out by Valdés et al. (2008) on fish scalestaken from this bay's deep-ocean sediments made it possible to recon-struct fluctuations in fish populations for the last 250 years and theirrelation to changes in biologic production and in the oxygenation ofthe water column.

The objective of this work is to reconstruct the ocean-climatic vari-ability during the last millennium and to determine its influence onpopulation fluctuations of the anchovy in the coastal area of theNorthern Humboldt Current System.

2. Sampling and analysis

In June 2009 a box corer of 225 cm2 and 1m longwas used to collecta sediment column of 54 cm long fromMejillones Bay (23° 1.974′S–70°27.255′O) at 80 m below the sea surface (Fig. 1). The sedimentary

Table 3ANOVA carried out to establish significant differences (P b 0.005) between the differentsedimentary phases. In bold are highlighted the variables with significant differences.

Temperature(°C)

Quartz(%)

COT(%)

C37 OI SDR

F 2.3 8.22 19.58 13.73 1.1 5.57P 0.086 0.001 0.001 0.001 0.352 0.001

structure was analyzed with a Quantum Medical digital X-ray equip-ment, power 55 Kv, at 1 m distance and with a 0.96 s exposure time.The chronology for the last 150 years was assessed by considering thenatural distribution of the excess 210Pb (Appleby and Oldfield, 1990),whereas for a longer time frame 14C dating was used (Vargas et al.,2007; Gutiérrez et al., 2009) and then these radiocarbon ages were cal-ibrated with the local 263 ± 60 years reservoir effect described byOrtlieb et al. (2011).

The mineral composition was determined with an FT-IR Perkin-Elmer 16F PC 8400S instrument. The Total Organic Carbon (TOC) con-tent and the Oxygen Index (OI) was measured by using the Rock-Eval6 pyrolysis method, with 1 mg of dry sediment, according to the meth-odology described by Lafargue et al. (1998). The concentration ofalkenones was determined with a Perkin-Elmer Auto System XL® gaschromatograph equipped with a flame-ionization detector (FID). Forthe lipid extraction the ASE 2000 (dionex) solvent accelerated extractor

Fig. 5.Amodified Van Krevelen diagram applied to the sedimentary column. The differentsymbols show the sedimentary units identified in the sample and the red line shows theoxidation pathway.

214 M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

was used, with which all lipids were separated from the sediment byusing dichloromethane–methanol (1:1) at 1100°. This extract was sep-arated into sub-fractions according by the procedure of Ternois et al.(1998). In brief, chromatographic columns were prepared by means ofPasteur pipettes that were plugged with glass fiber with an opening of100–200 μm. Then, 4.5 cm silica was added. This silica had been previ-ously activated at 110 °C for 24 h. Once the column was prepared, theextract was slowly injected and a series of solvents were applied toseparate them.

• Fraction 1: 2 ml of heptane (hydrocarbons)• Fraction 2: 1 ml of heptane + 2 ml of heptane:toluene (75:25)(PAHs*)

• Fraction 3: 2 ml of heptane: toluene (50:50) (esters)• Fraction 4: 2 ml of heptane:ethyl acetate (95:05) + 2 ml of heptane:ethyl acetate (90:10) (alkenones)

• Fraction 5: 2 ml of heptane:ethyl acetate (85:15) (alcohols)• Fraction 6: 2 ml of heptane:ethyl acetate (80:20) (sterols)• Fraction 7: 3 ml ethyl acetate + 3 ml of methanol (polar)• *PAH= Polycyclic Aromatic Hydrocarbons

The fractionswere collected in individual 4ml vials thatwere placedin a heating plate under a constant nitrogen flow to evaporate solvents.Once the solvents had evaporated, the fractions were refrigeratedbefore proceeding with the chromatographic analysis. Turbochrom®,software was used for data acquisition. The alkenone paleotemperaturecalculation was done by the methodology described by Prahl et al.(1988). A detailed description of the analysis method can be found inGrugel (2008). For the study of the anchovy scales the typical scale clas-sification for each species was used. These scales easily come off the fishand are foundwith no difficulty in sediments (Soutar, 1967; Soutar andIsaacs, 1974;DeVries and Pearcy, 1982; Shackleton, 1987; O'Connell andTunnicliffe, 2001). Typical scales for the most important species in thisstudy area are described by Valdés et al. (2008). The scales are charac-terized by their overall scale shape, the shape of focus, the appearance

Y1955 1960 1965 1970 1975

Ton

s

0

1e+5

2e+5

3e+5

4e+5

5e+5

6e+5

SDR

Anc

hovy

(N°

of s

cale

s cm

-2 y

ear-1

)*10

00

0

50

100

150

200

250 a)

b)

Fig. 6. Comparison of the SDR (Scale Deposition Rate) versus

of the anterior and posterior fields, and their radii (Salvatteci et al.,2012). Counting of fish scales was used to calculate the Scale DepositionRate (SDR) index:

SDR ¼ NBof scalescm−2 year−1� �

� 1000

A variance analysis was appliedwith theMinitab 14 software with asignificance level b0.005 to determine whether there are significantdifferences between the strata described and a Tukey analysis aposteriori was implemented for the most significant parameters.

Spectral analysis was performed to estimate the main periodicand/or quasi-periodic components of the paleoceanographic timeseries (temperature, anchovy SDR index, TOC, C37, OI) collected fromthe sediment samples. These analyses are also performed on the PDOtime series (Mantua et al., 1997), the NAO (Trouet et al., 2009), andthe solar irradiance index (Mann et al., 2005), with the aim of identify-ing frequencies equivalent to those found in the sample series, thus pro-viding an interpretive basis for the variations found in the data set.

Because the paleoceanographic series have irregular time spacingwith intervals of 4, 5 or 6 years, each of these series had to be adjustedto a cubic spline function to retrieve regular interpolated data every6 years (Emery and Thomson, 2004). As the stratigraphic time seriesdid not meet the stationary conditions, they were transformed into alogarithmic function type log(x + 1) before the spectral analysis sothat the series would remain stationary (Weedon, 2003). Then, theywere subjected to a spectral analysis consisting of the techniques ofFast Fourier Transformation from which a smoothed periodogram wasobtained as a spectral estimation using Daniell's window. Before doingthis, the series' mean value and trend were calculated. There was a 5%data tapering so as to soften the extremes of the series and a zero-padding of 128 data. Peak significance levelswere obtained after compar-ing them with the white noise spectrum (Emery and Thomson, 2004;Shumway and Stoffer, 2011). We recognize that the stratigraphic seriesare subject to other types of distortions due to the effect of variations in

ears (A.D)1980 1985 1990 1995 2000 2005

regional anchovy landings: a) SDR; b) regional landings.

215M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

the sediment deposition rates and/or bioturbation. However, the latterprocess is minimal to be absent for the Mejillones Bay sedimentsbecause of their dysoxia. These factors could also have an influence onpeak detection (Weedon, 2003). Also, the sampling interval and theseries size are two important factors to be considered in the spectral anal-ysis. In effect, to increment the spectral resolution it is necessary to in-crease the time series length (Weedon, 2003). The PDO, the NAO andthe solar irradiance index series have been subjected to the same proce-dures, working on evenly spaced series every 6 years, from the year1338 onwards, so as to be comparable with the time series of the proxies(Weedon, 2003).

3. Results

3.1. Chronology and lithology

The model used for 210Pb dating was the Constant Rate Sedimenta-tion (CRS) model, whereas for the 14C dating the Calib 6.1 programwas used. Once the data cleansing process was finished, both modelswere adjusted through a linear regression (R2 = 0.9982), by which anaverage deposition rate was calculated (0.08 cm year−1). The sedimen-tation rate indicates that the sedimentary column is 674 years old(Tables 1 and 2, Figs. 2 and 3). A similar sedimentation rate (0.131 ±

Fig. 7. SST and precipitation records during the last 700 years. (a) 10-point average of the “Noraverage of Ti% in Cariaco Basin (Haug et al., 2001). (c). Sea surface temperature anomaly recor

0.07 cm year−1) was obtained by Vargas et al. (2007) for a sample col-lected in 1998 in the same bay.

The radiographic imaging revealed different types of laminationswithin the sedimentary column, having alternations of light and darklayers with variable widths. The darker layers correspond to lessdense material and the lighter ones correspond to more dense material(Fig. 3). The stratification pattern is well expressed and sharply definedand exhibits no evidence of bioturbation related to benthic macrofauna(e.g. cracks or layer erosion) or physical disturbance owing to bayundercurrents or clear seismic events, the latter registered in other sam-ples collected in this bay, Vargas et al. (2005) indicate that severalseismic events that occurred in 1768 and 1543 AD generated loss ofmaterial in some sedimentary records, but they cannot be observed inour record. According to variations in the lithology and proxies, thecore could be subdivided into four stratigraphic units (Figs. 3 and 4).

3.2. Mineral fraction

The FTIR spectroscopy identified calcite, argonite, albite, silica andquartzwith a predominance of the latter. The variance analysis revealedsignificant differences in quartz content between the 4 stratigraphicunits identified in the samples (Table 3). In unit I quartz shows severalfluctuations, being the average for this unit 6%, whereas in unit 2 there

thern Hemisphere land error-in-variable (EIV) composite” (Mann et al., 2009). (b) 3-pointd of Mejillones Bay.

216 M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

is a gradual average increase in quartz concentration to the present day(6.2%). In unit 3 the same behavior unfolds with an increasing trend(9%). Finally, in unit 4 it is possible to identify an increase in the averagepercent quartz (10.3%).

3.3. Organic fraction

In Unit 1 there is a high variability in TOC percentage progressingtoward a diminishing trend (average: 4.6%); in unit II this tendencychanges toward a general rising one with a 4% average rise. Unit III is aperiod that exhibits varying fluctuations with a rising trend (4.9%).Finally, unit IV shows a significant increase in TOC percentage with anaverage of 5.8% (Fig. 4). These TOC averages corresponding to the differ-ent stratigraphic units exhibit significant differences (Table 3).

The Oxygen Index values in unit I show considerable fluctuation anda general average of 166 Co2/g TOC. In unit II there is a slight decreasewith an average of 166 Co2/g TOC. In unit III, there is a decrease withan average value of 162.8 Co2/g TOC. Finally, the OI decreases onceagain, showing an average of 162.2 Co2/g TOC. However, these differ-ences are not statistically significant (Table 3).

The alkenone concentrations in unit I have an average value of 5.4(μg g−1) and an increasing trend, whereas in unit II there is a decreasein the concentration with an average of 4.2 (μg g−1). Units III and IVhave an increase in the concentration of alkenones from 28.5 cm to0.5 cm with average values of 7.7 (μg g−1) and 16.1 (μg g−1), respec-tively. Significant differences exist in the concentration of alkenonesamong the different stratigraphic units (Table 3). After doing the post

Fig. 8. TOC anomaly (a) Callao Bay, Perú (Salvat

hoc comparisons (Tukey), it was determined that unit IV differs fromthe rest. The sea surface temperature, determined from the concentra-tions of alkenones, has an increasing trend in unit I with a mean valueof 19 °C. Unit 2 does not show a clear trend but has large temperaturefluctuations and an average of 19°. Unit III shows also an average of19 °C. Finally, unit IV also presents a decreasing trend with an averageof 18 °C (Fig. 4).

Significant differences were registered among the various sedimen-tary phases associated with the sea surface temperature determined bythe alkenones (Table 3). After doing the post hoc comparisons (Tukey),it was again determined that unit IV differs from the others.

3.4. Fish remains

Fish remains expressed by the SDR index show low values in unit Iwith a 12.9 average, whereas this index increased for units II, III and IVwith average values of 51.3, 71 and 87.4 respectively (Fig. 4). Thesemean values are significantly different, according to the variance analy-sis (Table 3). After doing the post hoc comparisons (Tukey) itwas deter-mined that unit IV again differs from the rest.

3.5. Spectral analysis

The temporal series of the PDO, the NAO and the solar irradianceindex show significant peaks in different periods linked to low frequen-cies. However, there are periodicities in the PDO of around 75 years(74.8 years) that can also be found in the anchovy, temperature, organic

teci et al., 2014). (b). Mejillones Bay, Chile.

217M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

carbon, C37 alkenone, and OI series at quite near the same value. At thesame time, 61.5 years periodicity in the PDO is also found in the NAOseries (61.6 years) and can be roughly observed in all the series ana-lyzed herein (anchovy, temperature, organic carbon, C37 alkenone andOI). Finally, the solar radiation periodicity of 83.2 years can be observedin all the series with the exception of the temperature proxy (Figs. 11and 12).

4. Discussion

4.1. Stratigraphy

The differentiation of the stratigraphic units is based on visual obser-vation and the concordance of this stratigraphy with the fluctuationsexhibited by the measured parameters (Vargas et al., 2000; Sifeddineet al., 2008). The laminations show different thicknesses that varyfrom 2 mm to 4 cm (Fig. 3). The thicker layers could correspond tolarge diatom remains (Coscinodiscus sp.), which have earlier beendescribed by Vargas et al. (2004) and Caniupán et al. (2009) who attri-bute this type of stratification to alternations in opal content. Usingthese properties, it is possible to divide the sediment column into 4stratigraphic facies: I (54 cm–44 cm; 1330–1460 AD), that is character-ized by presenting thick, not well defined layers; II (44–31.5 cm; 1460–1620 AD), that is characterized by thinner and well defined layers thatalternate in color between light and dark with a predominance of theformer (Fig. 3); III (31.5–10.5 cm; 1620–1880 AD) that is similar tothe second one but with a predominance of dark layers;. IV (10.5–0.5 cm; 1880–2009 AD), that contains an alternation of thick, lightand dark layers and is capped by a large light layer that is 3 cm thickapproximately (1–4 cm).

Although little evidence of tectonic disturbance exists in the sedi-ment column, Vargas et al. (2005) note that a seismic event is registeredin the bay sediments that probably corresponds to an earthquake thatoccurred in 1768. However, they also state that the great earthquakeof 1877 did not produce any evident perturbation in the sedimentarycolumn, probably because the Mejillones Peninsula drastically dissi-pated the energy associated to this event (Delouis et al., 1997).Although our record shows no evidence of this incident, a section ofsediment near the base of our sediment core that has no clear stratifica-tion can be considered a possible consequence of the seismic eventidentified in the middle of the 15th century by Vargas et al. (2005).

The main source of organic material that constitutes the sedimentsof Mejillones Bay is from pelagic production (Fig. 5). As noted byValdés et al. (2004), there is no significant continental contributionfrom rivers or rain runoff. The land bordering the bay is the barrenAtacama Desert, with no rivers and with an extremely low rain rate.

4.2. Local ocean-climatic fluctuations

4.2.1. Upwelling, productivity and oxidizing markersFlores-Aqueveque (2010) point out that the presence of quartz

particles in marine sediments inMejillones Bay clearly suggests a conti-nental contribution, and considering that there are no rivers in this areathat might transport lithogenic material from land to sea, deliveries ofthese components are closely connected to the southwest winds thatare responsible for transporting these substances to the bay and thatdrive the upwelling events that typify this area. The same authorsrelated the presence of these minerals in sediment traps to changes inthe intensity of winds along Mejillones Bay. These data were obtainedby comparing themineral flowwith the average wind force in differentstudy periods. Therefore, we can assume that an increase in quartzcontent recorded in our sediment samples suggests an increase ofwinds favorable to upwelling, mainly from 1800 to our day (Fig. 4).

The average TOC concentrations of the sediments analyzed in thesedimentary column are between 3.4 and 7% (Fig. 4), which repre-sent similar values to those yielded in previous studies in this bay

(Valdés et al., 2004, 2009; Vargas et al., 2004; Caniupán et al., 2009,Díaz-Ochoa et al., 2011). Moreover, these values are within therange of those reported for other high-productivity areas in Chile(Thamdrup and Canfield, 1996), and Perú (Sifeddine et al., 2008;Díaz-Ochoa et al., 2009; Gutiérrez et al., 2011). Research carried outby Valdés et al. (2009) and Guiñez et al. (2010) in relation to the surfacesediments collected at various depths in Mejillones Bay show that thetotal organic carbon percentage of deep-ocean sediments is particularlysensitive to OMZ intensification. Thus, TOC is better preserved in thedeepest areas of the bay, with values of 5 to 10% at 80 to 120 m waterdepth, as compared to a 0.7 to 3% at 0 to 35mwater depth. For this rea-son, the samples were collected in the best preserved areas of the baywith the aim of yielding a TOC record that would be in accordancewith the surface layers of the water column.

Total organic carbon is a mixture of primary and secondary pro-ductivity, thus accounting for the whole biological productivity andits oxidizing effect on thepotential preservationof deep-ocean sediments(Valdés et al., 2004). In contrast, alkenones account for only the pri-mary production done by the coccolithophores (Pichevin et al.,2004), which are typical organisms in Mejillones Bay, especially dur-ing high-productivity periods (Rodríguez et al., 1996).

Biological markers (TOC and C37) showed significant differences inthe average content recorded for each stratigraphic unit (Table 3) anda general tendency to increase in the sediment column upper layers.The increase suggests that in the past 700 years, the bay's biologicalproductivity has increased, especially since the 19th century (Fig. 4).Caniupán et al. (2009), also highlight that in the past two centuriesthere has been an increase in the concentration of alkenones in theMejillones Bay, thus suggesting a rise in phytoplankton productivityon a local scale, whereas Vargas et al. (2007) registered the same ten-dency in TOC content in the Mejillones Bay sediments during the lasttwo centuries. Considering that the sedimentary organic matter thatfalls on the sea floor is affected differently depending on the oxygen-ation conditions and that the origin of the organic matter in thesediments in the bay is phytoplanktonic (Fig. 4), the oxygen indexrepresents the amount of aerobic degradation of this material andallows us to determine the temporal variability experienced in theOMZ from our sedimentary records (Sifeddine et al., 2008; Gutiérrezet al., 2009; Valdés et al., 2009; Guiñez et al., 2010). More specifically,higher productivity generates more oxygen consumption in the watercolumn, generating a decrease of dissolved oxygen and lower oxidationindex (OI) (Valdés et al., 2004). Although the OI differences found in thesample sedimentary facies of Mejillones are not significant (Table 3),the correlation coefficient shows a negative interaction between theOI, the alkenones and the TOC (r2: −0.135; r2: −0.126 respectively).These findings strengthen an inverse behavior that relates productivitywith oxygen consumption. Meanwhile, the correlation between TOCand the alkenones is positive (r2: 0.678). This relation shows that bothindicators have a similar behavior associatedwith variability in the pro-ductivity. Thus, during the last 700 years, there have been fluctuationsin productivity that have brought about changes in the bay water oxy-gen, thereby intensifying the OMZ during the last centuries as a resultof an increase in productivity seen in unit IV (Fig. 4). When analyzingthe temporal fluctuations we can see that the period between 1330and 1460 AD is characterized by a relatively stable condition in termsof biological productivity and oxygenation of the water column,although with productivity levels much lower as compared to the restof the reconstructed series. Between 1620 and 1840 the productivity in-dicators uncouple and show different trends.Whereas the TOC tends todiminish, the alkenones increase. This situation suggests that althoughthe primary productivity increased during this period, the biologicalproductivity did not vary significantly and/or the potential preservationof organic matter was less due to a more oxygenated condition of thebay's water column as shown in the OI during this period. At presentand since 1840, although the biological productivity shows a generalsubstantial increase associated with a constant decrease in oxygen,

Tro

pica

l Sol

ar R

adia

tive

Forc

ing

(W m

-2)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

NA

O

-3

-2

-1

0

1

2

3

Years (AD)

1300 1350 1400 1450 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000

SDR

(A

ncho

vy)

-4

-2

0

2

4

6

8

PDO

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

SST

-Alk

enon

e (C

°)

-3

-2

-1

0

1

2

3

4

218 M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

Year (A.D)1904 1912 1920 1928 1936 1944 1952 1960 1968 1976 1984 1992 2000 2008

Paci

fic

Dec

adal

Osc

illat

ion

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Eng

raul

is r

inge

ns A

nom

aly

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Fig. 10. Comparison between the Pacific Decadal Oscillation (instrumental record, Mantua et al., 1997) versus the SDR of anchovy for the last 100 years. The dotted line corre-sponds to the PDO.

219M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

there has been a decrease in productivity and a greater oxygenation ofthe waters in the bay in the last 30 years.

Fluctuations in the biological productivity, the oxygenation, andupwelling suggest a local response to climatic events that haveaffected the planet during the last millennium. Especially importantwere the Medieval Climatic Anomaly (MCA), which extended fromthe 9th to the 14th century, and the Little Ice Age (LIA), which occurredfrom the 15th century through the 18th century, and forwhich there arepaleoenvironmental records on the Peruvian coast and the Chilean pla-teau (Haug et al., 2001; Sifeddine et al., 2008;Gutiérrez et al., 2009; Gayoet al., 2012; Salvatteci et al., 2014). Thus, the Mejillones sedimentaryrecord covers the pre-LIA period and LIA (1330–1500 A.D.) duringwhich the bay water was characterized by considerable fluctuations inoxygen content, enhanced southwest winds, and high biological pro-ductivity. After the end of this period and during the LIA, theseparameters show a gradual change, with low wind intensities, slightlymore oxygen content in water, and low biological productivity (Fig. 4).

When comparing this interpretation with the productivity condi-tions described for Perú by Salvatteci et al. (2014), we can say thatthe situations in both systems were different or did not respond simul-taneously to climatic variability before the regime shift at the beginningof the 19th century (Valdés et al., 2003; Sifeddine et al., 2008; Gutiérrezet al., 2009) (Fig. 4), and all this was a consequence of the displacementof the Pacific anticyclone (PAC), as described by Saavedra and Foppiano(1992). This repositioning brought about dry conditions around theCariaco Trench and El Niño type conditions along the Peruvian coasts,thus increasing rains and diminishing productivity (Figs. 7 and 8)(Salvatteci et al., 2014). In contrast, the consequent displacement ofthe ITCZ would not be as significant for the more southward locationof Mejillones Bay; therefore the upwelling intensity diminishes andthe sea surface temperature rises as a consequence of a decreasingPAC influence (Figs. 7 and 8). At the turn of the 19th century, the ITCZ,influenced by the latter change (PAC), shifted to the north, causing aproductivity increase in both systems. Therefore, we can infer thatpaleoclimatic variability reconstructed on a local scale in MejillonesBay is connected to both regional and global events, and althoughthey do not have the same characteristics in terms of environmental

Fig. 9. Comparative analysis of the different oscillations experienced by the ocean-climatethe anchovy SDR records in our samples.

conditions prevailing in the different geographical regions, they didoccur in the same time period.

4.2.2. Fluctuations of anchovy populationsAlthough fish scales are thought to bewell preserved inmarine sed-

iments, the possibility that they may be subject to degradation remainspossible. Scales are composed of hydroxyapatite (Ca10(PO4)6(OH)2)covered by an organic matrix surrounded by collagen fibers, and eachof these components is subject to degradation (Salvatteci et al., 2012).It has been shown that there is a loss of organic matter in the scalesfound in sediments relative to those on fish (Field et al., 2009). In oxy-genated sediments, acidification caused by oxidation of organic mattercan dissolve the biogenic apatite, thus affecting the preservation ofscales, whereas in suboxic and anoxic conditions, the acidificationdramatically diminishes (Schenau and De Lange. 2000). In the case ofMejillones Bay, the presence of an OMZ reduces the likelihood of degra-dation of fish remains, a situation that is favored by a minimal abrasionby sediments due to the lack of benthic fauna and the limited bacterialactivity (Valdés et al., 2008). Hence, this system constitutes a good envi-ronment for the reconstruction of former fish populations by using thescales or fish remains preserved in marine sediments (Gallardo, 1963;Milessi et al., 2005; Valdés et al., 2008).

Although different types of scales were recovered in the samples,mostly those of sardine and anchovy; we worked only with the latteras they were more abundant, therefore suggesting little dissolution(Valdés et al., 2008). A lack of sardine scales (another species of com-mercial significance) has been reported by Valdés et al. (2008) andDíaz-Ochoa et al. (2009) for this bay and also for the Peruvian coast(Gutiérrez et al., 2009). One of the reasons for the scarcity of sardinescales could be associated with the sardine biological parameters. Inthat respect, Yáñez et al. (1995), show that during the warm periodslike El Niño, food resources tend to move south, whereas in cold condi-tions they move to the north. This situation can directly affect theamount of sardines in Mejillones Bay owing to the upwelling eventsthat would be creating a thermal front and thus affecting the distribu-tion of this species in the study area, considering the optimal tempera-ture range that they require. Also, Yáñez (2003) (IFOP) highlight that

system versus the sea surface temperatures recorded in Mejillones Bay sediments and

220 M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

warmer conditions cause anchovies to move deeper into the ocean, asfar as 120mdeep,whereas in colder conditions they increase in numberas compared to the amount of sardines. Fluctuations in the SDR of theanchovy in the Mejillones sample present a pattern that, togetherwith the markers used, are in agreement with the stratigraphicunits. A linkage also exists between temperature and the SDR thatis expressed as an inversely proportional relation between both indica-tors (r2:−0.290), clearly seen in the fluctuations of the anchovy popu-lations associated with the temperature. The general tendency shows adecrease between 1330 and 1500 in which few scales are observed inthe anchovy records, which suggests a displacement of the anchovy asa consequence of a possible increase in temperature during this period.After this period and until 1610 there is afirst increase in the abundanceof this species. Subsequently and until 1840 there is a new great cycle(greater than the previous one), and finally, from 1840 to date, thereare shorter cycles, although with a larger abundance of the anchovy inthe area associated with a higher primary productivity and lower oxy-genation of the water column (Fig. 4). All this results from a change inthe climatic and oceanographic conditions present during the LIA,which are similar to those of El Niño in which production decreasedand the sea surface temperature increased relative to unit VI (Fig. 4),(Finney et al., 2010). These conditions changed by the end of the LIAwhen the ocean-climatic regime became more like La Niña phenome-non, which is muchmore favorable to the anchovy (Fig. 4). This changein the ecological conditions registered in the Mejillones record is inagreement with what has been reported by Vargas et al. (2007) andValdés et al. (2008) for this bay, and by Sifeddine et al. (2008) andGutiérrez et al. (2009), for the central-southern Peruvian coasts, which

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Rel

ativ

e Po

wer

a) Periodogram AnchovySDR: 1350 - 2004

1

2

3

45

6

Periods

1= 545.68 y2= 211.59 y3= 82.94 y4= 72.00 y5= 63.08 y6= 56.11 y

W.N.S

0.00

00.

005

0.01

00.

015

Rel

ativ

e Po

wer

c) Periodogram Organic Carbon (%):1344 - 2004

1

2

3

4

5

67

Periods

1= 307.20 y2= 163.27 y3= 106.06 y4= 86.67 y5= 74.86 y6= 65.31 y7= 53.58 y

W.N.S

0.0 0.1 0.2 0.3 0.4 0.5

0.0 0.1 0.2 0.3 0.4 0.5

Frequency (cp6y)

Frequency (cp6y)

Fig. 11. Spectral analysis for Mejillones Bay proxy time series (a) Anchovy SDR, (b) Sea SurfaceNoise Spectrum (WNS), and the frequency states for cycles per 6 years.

suggests that the northern region of the Humboldt Current ecosystemhas responded simultaneously to climatic fluctuations since the begin-ning of the 1820's.

During the historical period and mainly in the 20th century, theabundance of the anchovy, inferred from the presence of scales in theMejillones samples, shows a pattern inverse to that prevailing in thedata captured in northern Chile (Fig. 6). When the fishing of anchovyfirst started in 1960 the SDR was around 230, but in 1965 the SDRdiminished as the fishing effort on that species increases. In 1967the landings reach 300,000 tons, and the SDR is around 100 (Fig. 6).After 1974, there is a greater fishing effort which makes the SDRin the Mejillones sample reach an average of 41.1, followed by adecrease in the SDR until 2000 when it slightly increased (Fig. 6). Thissituation suggests that fishing effort activities have had a strong impacton the abundance of the anchovy in the area of Mejillones Bay (Fig. 6).

4.3. Local ocean-climatic fluctuations versus regional and global forces(spectral analysis)

The results of the spectral analysis (Figs. 11 and 12) show that theanchovy SDR, the temperature, the productivity, and the oxygenationof the waters in Mejillones Bay exhibit several fluctuation periodsthat are related to those in the solar radiation index, the PDO and NAOtime series (Fig. 9).

The solar radiation index determines that fluctuations in the solarradiation can have an impact on the Earth's climate in periods asso-ciated with cycles of the sun for different stretching durations (Grayet al., 2010). Among the most well-known is the 11 year cycle, which

0.0 0.1 0.2 0.3 0.4 0.50.00

000.

0010

0.00

200.

0030

Frequency (cp6y)

Rel

ativ

e Po

wer

b) Periodogram Temperature:1344 - 2004

1

2

3

4

56

Periods

1= 370.28 y2= 153.31 y3= 116.98 y4= 94.90 y5= 70.41 y6= 60.58 y

W.N.S

0.0

0.1

0.2

0.3

0.4

Rel

ativ

e Po

wer

d) Periodogram C37(ug/g):1344 - 2004

1

2

3

4

5

Periods

1= 292.05 y2= 124.16 y3= 98.50 y4= 81.87 y5= 58.37 y

W.N.S

0.0 0.1 0.2 0.3 0.4 0.5Frequency (cp6y)

Temperature, (c) Organic Carbon, and (d) C37. The straight line corresponds to theWhite

221M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

does not appear in the Mejillones data because the minimum periodthat can be detected by them is 12 years. However, the 83.19 year cyclewas in fact detected, and this can be associatedwith solar fluctuations of80 to 100 years, also known as the Gleissberg solar cycle (Yousef, 2000;Christensen and Lassen, 1991; Ogurtsov et al., 2002). This periodicity ispresent in all the markers of the sedimentary record with the exceptionof temperature. Hence, it is possible that the SST might not directlyrespond to these forces as it is also influenced by, for example, coldsubsurface currents that may modify the surface water layer duringcoastal upwelling. The similarity in the solar radiation cycles and thepaleoenvironmental markers in the Mejillones record suggests that thesolar activitywould exert a strong influence in the ocean-climatic condi-tions of Mejillones Bay, as was observed in tree-ring proxies in southernChile and in other proxies in several areas around the world (Yousef,2000; Rigozo et al., 2007).

The PDO exhibited two cycles, one of 74 years and the other of62 years (Fig. 12), and these were found in the Mejillones time series(Fig. 9). Mantua et al. (1997) point out that the PDO has two phases: awarm one and a cold one. During the warm phase, heavy precipitationoccurs in the North Pacific whereas in a negative phase precipitation in-tensifies in the interior of North America and in Hawaii. The PDO coldphase also coincides with anomalies in the negative temperatures ofthe Equatorial Zone, and this factor would indicate not only strong up-welling along the Equator but also enhanced coastal upwellings alongthe southeast Pacific coast (Mestas-Núñez and Miller, 2006). Theseauthors assign a 50 to 70 year duration to the PDOcycle, which is similarto that determined by Chávez et al. (2003) to explain the variabilities in

0.0 0.1 0.2 0.3 0.4 0.5

0.00

00.

001

0.00

20.

003

0.00

4

Frequency (cp6y)

Rel

ativ

e Po

wer

a) Periodogram Oxygen Index (mg C o2/g COT): 1338 - 2004

1

23

45

6

7

8

Periods

1= 337.5 y2= 155.95 y3= 118.35 y4= 97.19 y5= 83.48 y6= 72.12 y7= 58.61 y8= 48.53 y

W.N.S

0.00

0.05

0.10

0.15

Frequency (cp6y)

c) Periodogram NAO: 1338 - 1992

1

2

3

4

56

7

Periods

1= 648.0 y2= 287.37 y3= 189.37 y4= 119.86 y5= 90.94 y6= 61.57 y7= 45.62 y

W.N.S

0.0 0.1 0.2 0.3 0.4 0.5

Rel

ativ

e Po

wer

Fig. 12. Spectral analysis for the (a) Oxygen Index and climatological time series, (b) PDO, (c) Ntrum (WNS), and the frequency states for cycles per 6 years.

the abundance of sardine and anchovy in the coastal waters of Perú. Inthe last 100 years there is a phase lag between the anchovy index andthe instrumental PDO records (Mantua et al., 1997), showing thatthe PDO cold phase coincides with an increase of the anchovy due toenhanced coastal upwelling (Fig. 10). These facts are also shown inthe prevalence of positive anomalies in the solar radiation index(Fig. 9). An increase of solar activity would bring about a rise of theEarth's average surface temperature, and, considering the differencesbetween the continents and the oceans with regard to their heat capac-ities, an intensification of the temperature gradient between and seawould occur. In turn, this situation would influence the pressure gradi-ent between the high and low pressure systems, bringing about a pres-sure increase between them (Gill, 1982), especially in the easternborders of the oceans where high pressure systems, like the high pres-sure over the Eastern South Pacific, would prevail throughout the year(Saavedra and Foppiano 1992). Thus, an intensification of the easternocean high pressure systems would imply a strengthening of coastalwinds. In particular, on the Chilean coasts, this situation would causean increase of the south and southwestwinds,which are favorable to in-creasing coastal upwelling and causing a decrease of the SST (Vargaset al., 2007).

The NAO has a 62 year cycle, similar to that observed in theMejillones time series that fluctuates between 58 and 65 years(Fig. 12). The NAO index is determined by calculating the differentnormalized sea-level atmospheric pressures in Lisbon, Portugal, andStykkisholmur, Iceland (Hurrell, 1995). This potential teleconnectionbetween the North Atlantic trend and the data registered in the South

0.00

0.02

0.04

0.06

Frequency (cp6y)

b) Periodogram PDO: 1338 - 1992

1

2

3

4

5

6

Periods

1= 385.71 y2= 199.02 y3= 98.90 y4= 74.79 y5= 61.55 y6= 48.01 y

W.N.S

0.00

00.

002

0.00

40.

006

0.00

8

Frequency (cp6y)

d) Periodogram Solar IradianceIndex (W/m^2): 1338 - 2004

1

2

3

45

6

Periods

1= 535.12 y2= 243.23 y3= 164.89 y4= 128.39 y5= 101.39 y6= 83.19 y

W.N.S

0.0 0.1 0.2 0.3 0.4 0.5

0.0 0.1 0.2 0.3 0.4 0.5

Rel

ativ

e Po

wer

Rel

ativ

e Po

wer

AO and (d) Solar Irradiance Index. The straight line corresponds to theWhite Noise Spec-

222 M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

American western margins has been described before. For example,Gayo et al. (2012) suggest that the NAO has had an indirect influenceon fluctuations in the hydrologic cycle of the Chilean plateau duringthe last 2500 years. These authors suggest that during the NAO's coldphase there is a southward displacement of the ITCZ and of theBolivian High Pressure system, thus increasing the levels of moisturecoming from the Amazon region. This displacement of the ITCZ hasalso been invoked to explain the ocean-climatic fluctuations registeredduring the last thousand years on the Peruvian coast (Gutiérrez et al.,2009). The fact that the PDO and NAO have similar 62 year cyclessuggests a certain degree of teleconnection between the two events.Although historical time series have not shown a correlation betweenthe PDO and NAO indexes at an interannual time scale (Rogers, 1981),authors such as Enfield and Mayer (1997), and Polonsky et al. (2004),suggest different ways of connecting both cycles at other times. Forexample Enfield and Mayer (1997) agree that the North Atlanticwarms in response to ENSO in the equatorial Pacific but with a delaybetween 1 and 2 seasons due to the ocean's thermal inertia. They alsoadd that the North Atlantic reaction to ENSO has seasonal behavior,being stronger in the boreal spring and beginning of summer andweak-er during autumn and early winter. Moreover, Polonsky et al. (2004),indicate that multidecadal variations of NAO-related thermohalinecirculation can impact the ENSO event not only directly through thechange of the basic state of equatorial ocean, but also indirectly throughthe change of the temperature Asia-Pacific contrasts and followingENSO–monsoon interaction.

Finally, the findings of this study suggest that the PDO and the NAO,as well as the biogeochemical markers of the Mejillones record, exhibitperiodicities like those found in the Gleissberg solar cycle, which indi-cates that global solar intensity plays an important role in local ocean-climatic processes, thus implying the existence of a teleconnectionbetween remote regions.

5. Conclusions

Variations in a suite of six paleoceanographic proxies show thatMejillones Bay has been under the influence of different ocean-climatic regimes during the last 700 years. Among these, we can spe-cifically identify the LIA (1500–1850)when El Niño conditions prevailedwith low productivity, high concentration of dissolved oxygen, and adecrease in the amount of anchovy. After this period, a temperaturedecrease and increases of the upwelling events, of the productivity,and of coldwaterfish species such as the anchovy occurred.We observean inverse relation between the abundance of the anchovy and thePacific Decadal Oscillation, expressed as an increase of this species dur-ing the cold PDOphase and a decrease during thewarmPDOphasewithalternating periods of 25 and 30 years for each phase.

Spectral analysis of the time series found in the Mejillones recordand the mechanisms of climatic change examined in this study exhibitperiodicities that suggest that the 80 to 100 year Gleissberg solar cycleis themain factor in local climatic variability that also seems to be influ-enced by the PDO and the NAO.

Acknowledgment

Thisworkwasfinanced byMECESUPANT0711project andCONICYTscholarship grant 2409104. Special thanks are given to Dr. Luc Ortlieb(IRD France), to the science team of the Laboratory of SedimentologyandPaleoenvironments of theUniversity of Antofagasta, and tomagisterVicente Ferreira for his support in helping to collect the samples.We alsothank Juan Carlos Leon for his support in taking radiographic imagesof the sedimentary box corer at the clinical laboratory “Blanco”,Antofagasta, Chile, and Sabrina C. Dávila for doing the English transla-tion. Finally we thank the two anonymous reviewers and the editorfor their help in improving this manuscript with their suggestions.

Appendix A. Supplementary data

Supplementary data associated with this article can be found in theonline version, at http://dx.doi.org/10.1016/j.palaeo.2014.08.026. Thesedata include Google maps of the most important areas described inthis article.

References

Alheit, J., Bernal, P., 1993. Effects of physical and biological changes on the biomass yieldof the Humboldt current system. In: Sherman, K., Alexander, L.M., Gold, B. (Eds.),LargeMarine Ecosystem—Stress, Mitigation, and Sustainability. American Associationfor the Advancement of Science, pp. 53–68.

Aliaga, B., Gómez, S., Neira, S., 2001. Análisis bioeconómico de la pesquería de la sardina(Sardinops sagax) y la anchoveta (Engraulis ringens) de la zonanorte de Chile. Investig.Mar. Valparaíso 29 (2), 15–23.

Appleby, P., Oldfield, F., 1990. The Use of Nuclear Techniques in Sediment Transport andSedimentation. UNESCO, Paris, pp. 131–167.

Avaria, S., Muñoz, P., 1982. Composición y biomasa del fitoplancton marino del norte deChile en diciembre de 1980 (operación oceanográfica MARCHILE XI-ERFEN II).Cienc. Tecnol. Mar CONA 6, 5–36.

Baumgartner, T., Soutar, A., Ferreira, V., 1992. Reconstruction of the history of pacific sar-dine and northern anchovy populations over the past two millennia from sedimentsof the Santa Barbara Basin, California. California Cooperative Oceanic Fisheries Inves-tigation Reports 33, pp. 24–40.

Bernal, P., Robles, F., Rojas, O., 1983. Variabilidad física y biológica en la región meridionaldel sistema de corrientes Chile, Perú. FAO Fish. Rep. 291, 683–711.

Caniupán, M., Villaseñor, T., Pantoja, S., Lange, C., Vargas, G., Muñoz, P., Salamanca, M.,2009. Sedimentos laminados de la Bahía Mejillones como registro de cambiostemporales en la productividad fitoplanctónica de los últimos ~200 años. Rev. Chil.Hist. Nat. 82, 83–302.

Castilla, J., Lagon, N., Guiñez, R., Lalgier, P., 2002. Embayments and nearshore retention ofplankton: the Antofagasta Bay and other examples. In: Castilla, J., Largier, J. (Eds.), TheOceanography and Ecology of the Nearshore and Bays in Chile. Ediciones UniversidadCatólica de Chile, Santiago, Chile, pp. 179–203.

Chávez, F., Ryan, J., Lluch-Cota, S., Niquen,M., 2003. Fromanchovies to sardines and back; cli-mate, fish, ocean productivity, and atmospheric carbon dioxide. Science 299, 217–221.

Christensen, F., Lassen, E., 1991. Length of the Solar Cycle: An indicator of solar activityclosely associated with climate, Science. New Series Vol. 254, 698–700.

Daneri, G., Dellarossa, V., Quiñones, R., Jacob, B., Montero, P., Ulloa, O., 2000. Primary pro-duction and community respiration in the Humboldt Current System off Chile andassociated oceanic areas. Mar. Ecol. Prog. Ser. 197, 41–49.

DeVries, T., Pearcy, W., 1982. Fish debris in sediments of the upwelling zone off centralPeru: a late Quaternary record. Deep-Sea Res. 28, 87–109.

Díaz-Ochoa, J., Lange, C., Pantoja, S., De Lange, J., Gutiérrez, D.,Muñoz, P., Salamanca,M., 2009.Preservation of fish scales in sediments from off Callao, central Peru. Deep-Sea Res. II 56,1124–1135.

Díaz-Ochoa, J., Pantoja, S., De Lange, G., Lange, C., Sánchez, G., Acuña, V., Muñoz, P., Vargas,G., 2011. Oxygenation variability in Mejillones Bay, off northern Chile, during the lasttwo centuries. Biogeosciences 8, 137–146.

Emery, W.J., Thomson, R.E., 2004. Data Analysis Methods in Physical Oceanography,Second and Revised Edition. Elsevier B.V., Amsterdam (619 pp.).

Enfield, D.B., Mayer, D., 1997. Tropical Atlantic sea surface temperature variability and itsrelation to El Niño-Southern Oscillation. J. Geophys. Res. 102, 929–945.

Escribano, R., 1998. Population dynamics of Calanus chilensis in the Chilean EasternBoundary Humboldt Current. Fish. Oceanogr. 7 (3/4), 245–251.

Escribano, R., Morales, C., 2004. Sistemas de surgencia costera. Biología Marina yoceanografía: conceptos y procesos Capitulo 21. Tomo II. , (683 pp.).

Field, D., Baumgartner, T., Ferreira, V., Gutierrez, D., Lozano-Montes, H., Salvatteci, R.,Soutar, A., 2009. In: Checkley, D., Roy, C., Alheit, J., Oozeki, Y. (Eds.), Variability fromscales in marine sediments and other historical recordsClimate Change and 823Small Pelagic Fish 822. Cambridge University Press, pp. 45–63.

Finney, B., Alheit, J., Emeis, C., Field, D., Gutierrez, D., Struck, U., 2010. Paleoecological studieson variability in marine fish populations: a long-term perspective on the impacts ofclimatic change on marine ecosystems. J. Mar. Syst. 79, 316–326.

Fitch, J., 1969. Fossil records of certain schooling fishes of the California current system.California Cooperative Oceanic Fisheries Investigation Reports. 13, pp. 71–80.

Flores-Aqueveque, V., 2010. Modelling the Aeolian Transport Processes Implications inthe Paleoclimate of the Coastal Atacama Desert. Universidad de Chile Facultad deCiencias y Matematicas, Departamento de Geologia.

Fuenzalida, R., Schneider, W., Garcés-Vargas, J., Bravo, L., Lange, C., 2009. Vertical andhorizontal extension of the oxygen minimum zone in the eastern South PacificOcean. Deep-Sea Res. II 56, 992–1003.

Gallardo, A., 1963. Notas sobre la densidad de la fauna bentonica en el sublitoral del nortede Chile. Gayana (Chile) 10, 1–15.

Gayo, E., Latorre, C., Santoro, C.,Maldonado, A., De Pol-Holz, R., 2012.Hydroclimate variabilityin the low-elevation Atacama Desert over the last 2500 yr. Clim. Past 8, 287–306.

Gill, A.E., 1982. Atmosphere–ocean dynamics. International Geophysics Series Vol. 30.Academic Press, New York (645 pp.).

González, H., Daneri, E., Figueroa, D., Iriarte, J., Fevre, Le, Pizarro, G., Quiñones, R., Sobarzo,M., Troncoso, A., 1998. Producción primaria y su destino en la trama trófica pelágica yocéano profundo e intercambio océano-atmósfera de CO2 en la zona norte de laCorriente de Humboldt (23°S): posibles efectos de evento El Niño, 1997–1998 enChile. Rev. Chil. Hist. Nat. 71, 429–458.

223M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

Gray, L., Beer, J., Geller, M., Haigh, J., Lockwood, M., Matthes, K., Cubasch, U., Fleitmann, D.,Harrison, G., Hood, L., Luterbacher, J., Meehl, G., Shindell, D., van Geel, B., White, W.,2010. Solar influence on climate. Rev. Geophys. 48, RG 4001. http://dx.doi.org/10.1029/2009RG000282.

Grugel, 2008. La sédimentation organique associée à deux systèmes d'upwelling enAmérique du Sud tropicale: implications paléocéanographiques et paléoclimatiquesau cours de l'Holocène. Université d'orléans.

Guiñez, M., Valdés, J., Sifeddine, A., 2010. Variabilidad espacial y temporal de la materiaorgánica sedimentaria, asociada a la Zona deMínimo Oxígeno (ZMO), en un ambientecostero del norte de la corriente de Humboldt, bahía de Mejillones, Chile. Lat. Am. J.Aquat. Res. 38 (2), 242–253.

Gutiérrez, D., Sifeddine, A., Field, D., Ortlieb, L., Vargas, G., Chávez, F., Velazco, F., Ferreira,V., Tapia, P., Salvatteci, R., Boucher, H., Morales, M., Valdés, J., Reyss, J., Campusano, A.,Boussafir,M., Mandeng-Yogo,M., García, M., Baumgartner, T., 2009. Rapid reorganiza-tion in ocean biogeochemistry off Peru towards the end of the Little Ice Age. Biogeo-sciences 6, 835–848.

Haug, H., Hughen, A., Sigman, M., Peterson, C., Róohl, U., 2001. Southwardmigration of theIntertropical Convergence Zone through the Holocene. Science 293, 1304–1308.

Helly, J., Levin, L., 2004. Global distribution of naturally occurring marine hypoxia oncontinental margin. Deep-Sea Res. I 51, 1159–1168.

Hunter, J., Alheit, J., 1995. International GLOBEC small pelagic fishes and climate changeprogram. GLOBEC report No. 8 (72 pp).

Hurrell, J.W., 1995. Decadal trends in the North Atlantic oscillation: regional temperaturesand precipitation. Science 269, 676–679.

Iriarte, J., Pizarro, G., Troncoso, V., Sobarzo, M., 2000. Primary production and biomasssize-fractioned phytoplankton off Antofagasta, Chile (23–24°S) during pre-El Niñoand El Niño 1997. J. Mar. Syst. 26, 37–51.

Lafargue, E., Marquis, E., Pillot, D., 1998. Rock-Eval 6 applications in hydrocarbon explora-tion, production, and soil contamination studies. Revue de L´Institut Francais duPétrole 53 (4), 421–473.

Langue, C., Burke, S., Berger, W., 1990. Biological production off southern California islinked to climatic change. Clim. Chang. 16, 319–329.

Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., 2005. Volcanic and solar forcing of thetropical Pacific over the past 1000 years. J. Clim. 18, 417–456 (February 1).

Mann, M.E., Zhang, Z., Rutherford, S., Bradley, R.S., Hughes, M.K., Shindell, D., Ammann, C.,Faluvegi, G., Ni, F., 2009. Global signatures and dynamical origins of the Little Ice Ageand Medieval Climate Anomaly. Science 326, 1256–1260.

Mantua, N.J., Hare, S.R., Zhang, Y., Wallace, J.M., Francis, R.C., 1997. A Pacific interdecadalclimate oscillation with impacts on salmon production. Bull. Am. Meteorol. Soc. 78,1069–1079.

Marín, V., Olivares, G., 1999. Estacionalidad de la productividad primaria en BahíaMejillones del Sur (Chile): una aproximación proceso-funcional. Rev. Chil. Hist. Nat.72, 629–641.

Marín, V., Rodiguez, L., Vallejo, L., Fuenteseca, J., Oyarce, E., 1993. Efecto de la surgenciacostera sobre la productividad primaria primaveral de bahía de Mejillones del Sur(Antofagasta, Chile). Rev. Chil. Hist. Nat. 66, 479–491.

Marín, V., Delgado, L., Escribano, R., 2003. Upwelling shadows atMejillones Bay (northernChilean coast): a remote sensing in situ analysis. Investig. Mar. 31 (2), 47–55.

Mestas-Núñez, A., Miller, A., 2006. Interdecadal variability and climate change in theeastern tropical Pacific: a review. Prog. Oceanogr. 69 (2006), 267–284.

Milessi, A., Sellanes, J., Gallardo, V., Langue, C., 2005. Osseous skeletal material and fishscales inmarine sediments under the oxygenminimumzone off northern and centralChile. Estuar. Coast. Shelf Sci. 64, 185–190.

Navea, E., Miranda, O., 1980. Ciclo anual de las condiciones oceanográficas en Mejillonesdel Sur. Rev. Biol. Mar. (Chile) 17, 97–133.

O’Connell, J.M., Tunnicliffe, V., 2001. The use of sedimentary fish remains for interpreta-tion of long-term fish population fluctuations. Marine Geology 174, 177–195.

Ogurtsov, M., Nagovitsyn, Y., Kocharov, E., Jungner, H., 2002. Long-period cycles ofthe sun’s activity recorded in direct solar data and proxies. Solar Physics 211,371–394.

Ortlieb, L., Escribano, R., Follegati, R., Zuñiga, O., Kong, I., Rodriguez, L., Valdes, J.,Iratchet, P., Guzmán, N., 2000. Ocean-climatic changes during the last2000 years in a hypoxic marine environment of Northern Chile (23°S). Rev. Chil.Hist. Nat. 73, 221–242.

Ortlieb, L., Vargas, G., Saliège, J.-F., 2011. Marine radiocarbon reservoir effect along the north-ern Chile–southern Peru coast (14–24°S) throughout the Holocene. Quat. Res. 75,91–103.

Overland, J., Percival, D., Mofjeld, H., 2006. Regime shift and red noise in the North Pacific.Deep-Sea Res. I 53, 582–588.

Pichevin, L., Bertrand, P., Boussafir, M., Disnar, J., 2004. Organic matter accumulation andpreservation controls in a deep seamodern environment: an example fromNamibianslope sediments. Org. Geochem. 35, 543–559.

Polonsky, A., Basharin, D., Voskresenskaya, E., Worley, S., Yurovsky, A., 2004. Relationshipbetween the North Atlantic oscillation, Euro-Asian climate anomalies and Pacificvariability. Pac. Oceanogr. 2 (1–2).

Polovina, J., 2004. Climate variation, regime shifts, and implications for sustainable fisher-ies. Bull. Mar. Sci. 7413.

Prahl, F., Muehlhausen, L., Zahnle, D., 1988. Further evaluation of long-chain alkenones asindicators of paleoceanographic conditions. Geochem. Cosmochem. Acta 52,2303–2310.

Rigozo, N., Nordemann, D., Evangelista da Silva, H., Pereira de Souza, M., Echerc, E., 2007.Solar and climate signal records in tree ring width from Chile (AD 1587–1994). Plan-etary and Space Science 55, 158–164.

Rodríguez, L., Escribano, R., 1996. Bahía de Antofagasta y Bahía de Mejillones del Sur:observaciones de la temperatura, penetración de la luz, biomasa y composiciónfitoplanctónica. Estud. Oceanol. 15, 75–85.

Rodríguez, L., Zárate, O., Oyarce, E., 1986. Producción primaria del fitoplancton y surelación con la temperatura, oxigeno, nutrientes y salinidad en la bahía de Mejillonesdel Sur. Revista de Biologia Marina, Valparaíso 22, 1–29.

Rogers, J.C., 1981. Spatial variability of seasonal sea-level pressure and 500-mb heightanomalies. Mon. Weather Rev. 109, 2093–2106.

Saavedra, N., Foppiano, A., 1992. Contribución a la cinemática del anticiclón del PacíficoSur. Geoacta 19, 95–110.

Salvatteci, R., Field, D., Baumgartner, T., Ferreira, V., Gutierrez, D., 2012. Evaluating fishscale preservation in sediment records from the oxygen minimum zone off Peru.Paleobiology 38 (1), 52–78.

Salvatteci, R., Gutiérrez, D., Field, D., Sifeddine, A., Ortlieb, L., Bouloubassi, I., Boussafir,M., Boucher, H., Cetin, F., 2014. The response of the Peruvian Upwelling Ecosystemto centennial-scale global change during the last two millennia. Climate Past 10,1–17.

Schenau, J., De Lange, J., 2000. A novel chemical method to quantify fish debris in marinesediments. Limnol. Oceanogr. 45, 963–971.

Serra, R., 1983. Changes in the abundance of pelagic resources along the Chilean coast.FAO Fish. Rep. 291 (2), 255–284.

Shackleton, L., 1987. A comparative study of fossil fish scales from three upwellingregions. S. Afr. J. Mar. Sci. 5, 79–84.

Shumway, R.H., Stoffer, D.S., 2011. Time Series Analysis and its Application. With R exam-ples. Third examples. Springer, New York (596 pp.).

Sifeddine, A., Gutierrez, D., Ortlieb, L., Boucher, H., Velazco, F., Field, D., Vargas, G., Boussafir,M., Salvatteci, R., Ferreira, V., García, M., Valdes, J., Caquineau, S., Mandeng Yogo,M., Cetin, F., Solis, J., Soler, P., Baumgartner, T., 2008. Laminated sediments fromthe central Peruvian continental slope: a 500 year record of upwelling systemproduc-tivity, terrestrial runoff and redox conditions. Prog. Oceanogr. 79, 190–197.

Silva, N., 1983.Masas de agua y circulación en la región norte de Chile. Latitudes 18o S-32o

S (Operación oceanográfica MarChile XI- ERFEN II). Ciencia y Tecnología del MarCONA (Chile) 7, 47–84.

Silva, N., Sievers, H., 1981. Masas de agua y circulación en la región de la rama costerade la corriente de Humboldt latitudes 18o S–33o S. (Operación oceanográficaMarChile X - ERFEN Y). Cienc. Tecnol. Mar CONA 5, 5–50.

Soutar, A., 1967. The accumulation of fish debris in certain California coastalsediments. California Cooperative Oceanic Fisheries Investigation Reports 11,pp. 136–139.

Soutar, A., Isaacs, J., 1969. History of fish populations inferred from fish scales in anaerobicsediments off California. California Cooperative Oceanic Fisheries InvestigationReports 13, pp. 63–70.

Soutar, A., Isaacs, J., 1974. Abundance of pelagic fish during the 19th and 20th centuries asrecorded in anaerobic sediment off the Californias. Fish. Bull. 72, 257–273.

Steele, J., 1998. From carbon flux to regime shift. Fish. Oceanogr. 7, 176–181.Strub, P., Mesias, J., Montecino, V., Rutllant, J., Salinas, S., 1998. Coastal ocean circulation off

western South America. Coastal segment. In: Robinson, A.R., Brink, K.H. (Eds.), vol.11. Wiley and Sons, pp. 273–313 (7888).

Takasuka, A., Oozeki, Y., Kubota, H., Lluch-Cota, S., 2008. Contrasting spawning tempera-ture optima: why are anchovy and sardine regime shifts synchronous across theNorth Pacific? Prog. Oceanogr. 77, 225–232.

Ternois, Y., Sicre, M.-A., Boireau, A., Beaufort, L., Miquel, J.-C., Jeandel, C., 1998. Hydrocar-bons, sterols and alkenones in sinking particles in the Indian Ocean sector of theSouthern Ocean. Organic Geochemistry 28, 489–501.

Thamdrup, B., Canfield, D., 1996. Pathways of carbon oxidation in continental margin sed-iments off central Chile. Limnol. Oceanogr. 41, 1629–1650.

Trouet, V., Esper, J., Graham, N.E., Baker, A., Scourse, J.D., Frank, D.C., 2009. Persistentpositive North Atlantic oscillation mode dominated the medieval climate anomaly.Science 324, 78–80. http://dx.doi.org/10.1126/science.1166349 (3).

Tunnicliffe, V., O'Connell, J., Mcquoid, M., 2001. A Holocene record of marine fish remainsfrom the Northeastern Pacific. Mar. Geol. 174, 197–210.

Valdés, J., 2004. Evaluación de metales redox-sensitivos como proxies depaleoxigenacion en un ambiente marino hipoxico del norte de Chile. Rev. Chil.Hist. Nat. 77, 121–138.

Valdés, J., López, L., Lomónaco, S., Ortlieb, L., 2000. Condiciones paleoambientales desedimentación y preservación de material orgánica en bahía de Mejillones del Sur(23° S), Chile. Rev. Biol. Mar. Oceanogr. 35 (2), 169–180.

Valdés, J., Sifeddine, A., Lalllier-Verges, E., Ortlieb, L., 2004. Petrographic andgeochemical study of organic matter in surficial laminated sediments from anupwelling system (Mejillones del Sur Bay, Northern Chile). Org. Geochem. 35,881–894.

Valdés, J., Ortlieb, L., Gutiérrez, D.,Marinovic, L., Vargas, G., Sifeddine, A., 2008. A 250 years–sedimentary record of Sardine and Anchovy scale deposition in Mejillones Bay, 23° S,Northern Chile. Prog. Oceanogr. 198–207.

Valdés, J., Sifeddine, A., Ortlieb, L., Pierre, C., 2009. Interplay between sedimentaryorganic matter and dissolved oxygen availability in a coastal zone of theHumboldt Current System; Mejillones Bay, northern Chile. Mar. Geol. 265,157–166.

Vargas, G., Ortlieb, L., Rutllant, J., 2000. Aluviones históricos en Antofagasta y su relacióncon eventos El Niño/Oscilación del Sur. Rev. Geol. Chile 27 (2), 155–174.

Vargas, G., Ortlieb, L., Pichón, J., Bertaux, J., Pujos, M., 2004. Sedimentary facies and highresolution primary production inferences from laminated diatomaceous sedimentsoff northern Chile (23° S). Mar. Geol. 211, 79–99.

Vargas, G., Ortlieb, L., Chapron, J., Valdés, J., Marquardt, C., 2005. Paleoseismic interfer-ences from a high-resolution marine sedimentary record in northern Chile (23° S).Tectonophysics 399, 381–398.

Vargas, G., Pantoja, S., Rutllant, J., Lange, C., Ortlieb, L., 2007. Enhancement of coastalupwelling and interdecadal ENSO-like variability in the Peru–Chile Current sincelate 19th century. Geophys. Res. Lett. 34 (L13607).

224 M. Guiñez et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 415 (2014) 210–224

Weedon, G., 2003. Time series Analysis and Cyclostratigraphy. Examining StratigraphicRecords of Environmental Cycles. Cambridge University Press, New York(259 pp).

Yáñez, E., 2003. Análisis integrado histórico ambiente – recursos, I y II Regiones. ProyectoFIP N° 2003–33.

Yáñez, E., González, A., Barbieri, M., 1995. Estructura térmica superficial del mar asociadaa la distribución espacio-temporal de sardina y anchoveta en la zona norte de Chileentre 1987 y 1992. Investig. Mar. Valparaíso 23, 123–147.

Yousef, S.M., 2000. The Solar Wolf–Gleissberg Cycle and its Influence on the Earth.ICEHM2000. Cairo University, Egypt, pp. 267–293.