land-fast ice off adélie land (antarctica): short-term variations in nutrients and chlorophyll just...

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Journal of Marine System

Land-fast ice off Adelie Land (Antarctica): short-term variations in

nutrients and chlorophyll just before ice break-up

C. Riaux-Gobina,*, P. Treguerb, G. Dieckmannc, E. Mariaa, G. Vetiona, M. Poulind

aCNRS, Laboratoire d’Oceanographie Biologique, 66650 Banyuls/mer, FrancebCNRS, IUEM, Technopole Brest-Iroise, 29280 Plouzane, France

cAlfred Wegener Institut fuer Polar und Meeresforschung Am, 27570 Bremerhaven, GermanydResearch Division, Canadian Museum of Nature, Ottawa, ON K1P 6P4, Canada

Received 21 January 2004; accepted 26 August 2004

Available online 14 November 2004

Abstract

This study focused on the short-term variations of sea ice microalgal biomass and nutrients, in Adelie Land coastal area

(Antarctica). The annual land-fast ice, bplatelet ice-likeQ layer (PLI) and under-lying seawater were sampled during the 1999

austral spring. The study was conducted during 33 days preceding the ice break-up, with a daily sampling when the

meteorological conditions were favourable. Time-series for salinity, chlorophyll a (Chl a), NH4+, NO2

�, NO3�, PO4

� and Si(OH)4are shown. We also provide satellite data and meteorological variables for the same period. During the study period, the solid

ice thickness varied from 1.47 to 1.05 m. Pigments were concentrated in bottom ice, but progressively invaded the PLI. Phaeo a

increased in the PLI during the last weeks, in parallel with increasing NO2� concentration. Si(OH)4, in lowest concentrations in

bottom ice, increased progressively in the under-ice water (UIW) and PLI, this was because of offshore water inputs. NH4+

concentrations were high in every sea ice component (particularly in the bottom ice) and were inversely correlated to pigments

in the bottom ice. NH4+ concentrations progressively increased in the PLI and underlying seawater just before the break-up. In

the bottom ice, PO4� concentrations were related to high pigment concentrations, but with a short lag close to the break up

period, indicating in situ regeneration. Neither NO3� nor NH4

+ concentrations were exhausted in the bottom ice. NO2� and NH4

+

concentrations increased in PLI and under-ice water just before the break-up period, which might indicate strong inorganic

nitrogen recycling in land-fast ice. Approximately 0.4 kmol km�1 linear coast of NH4+ (1 kmol NO3

� and 2 kmol PO4�) were

released to the under-ice seawater during break-up, along with 0.12 tons km�1 Chl a (9.6 tons POC km�1 equivalent). These

nutrient sea ice inputs to the coastal zone waters, during the ice recession and break-up, may vary annually depending upon the

local meteorological conditions that control ice formation, duration of ice cover and melting.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Annual land-fast ice; Time-series; Break-up; Nutrients; Sympagic biomass

0924-7963/$ - s

doi:10.1016/j.jm

* Correspondi

E-mail addr

s 55 (2005) 235–248

ee front matter D 2004 Elsevier B.V. All rights reserved.

arsys.2004.08.003

ng author. Tel.: +33 4 68887308; fax: +33 4 68887395.

ess: [email protected] (C. Riaux-Gobin).

C. Riaux-Gobin et al. / Journal of Marine Systems 55 (2005) 235–248236

1. Introduction

The biogeochemical characteristics of Antarctic

land-fast ice have been mainly investigated on multi-

year sea ice environments whereas annual land-fast ice

has been less documented. Recent studies on fast ice,

however, have focused on platelet ice layer and

highlight the importance of both nutrients and pigments

(i.e., Sullivan et al., 1982; Arrigo et al., 1993, 1995).

Whereas these variables/parameters seem highly var-

iable within site and season, it has been demonstrated

that the fast ice is related to high microalgal biomass

and production, and high nutrient regeneration (Tho-

mas and Papadimitriou, 2003; Arrigo, 2003).

To quantify the fast ice contribution to the enrich-

ment of the underlying water masses and benthos at

spring, researchers have assessed and reported the

nutrient and particulate organic matter inputs to the

coastal zone waters (i.e., Palmisano and Sullivan, 1983;

Matsuda et al., 1990; McMinn et al., 2000; Thomas et

al., 2001; Leventer, 2003). In Antarctic coastal zones, 2

or 3 weeks after sea ice break-up, a phytoplankton

bloom generally takes place. In Adelie Land, a study

already has been conducted after sea ice break-up, in

open water, and the spatial repartition of the phyto-

plankton described (Fiala and Delille, 1992). However,

neither the initiation nor the development of the bloom

Fig. 1. Adelie Land position on Antarc

itself was studied. It is of interest to evaluate the

contribution of the melting of fast ice and platelet ice to

this process. Indeed, it has been demonstrated that the

fast ice algae may contribute to the pelagic bloom (as a

seeding process; cf. in Ellis Fjord, eastern Antarctica,

McMinn, 1996), based on the similarity between fast

ice algae and pack ice diatoms. Our previous inves-

tigations at Adelie Land on small polynya and leads just

before the break up period (EPONTA 1995) showed

that the under-ice phytoplankton is composed of some

sedimented ice algae but also of other cells such as

Chaetoceros (encysted cells and vegetative colonies)

that were not present in the ice.

The annual land-fast ice of Adelie Land evidenced

high sympagic productivity (Riaux-Gobin et al.,

2000a,b; and references therein), similar or higher

than most of those previously reported (Arrigo, 2003).

During bEPONTA 1995Q, we studied the nutrients and

pigment biomass along a coast to offshore transect,

highlighting (1) a high sea ice sympagic biomass and

high nitrogen concentrations in the sea ice, partic-

ularly the bplatelet ice-likeQ layer (PLI), (2) a marked

coast to offshore decreasing gradient and a probable

bmass effectQ and (3) an apparent uncoupling between

the cycles of nitrogen and silicon.

In this paper, we report results from bEPONTA1999Q focusing particularly on the short-term varia-

tica and time-series station (R1).

C. Riaux-Gobin et al. / Journal of Marine Systems 55 (2005) 235–248 237

bility in nutrients and pigment biomass concentra-

tions, at a coastal land-fast ice station, during the 5-

week period that preceded the break-up. Specifically,

we studied the variations of dissolved nitrogen (NH4+,

NO3�, NO2

�), and of silicate [Si(OH)4] and phosphate

(PO4�). Compared to EPONTA 1995, significant

differences were observed in the conditions and

lasting of the ice cover and break-up conditions.

Nevertheless, the physical structure of the ice and the

presence of the sympagic layer were more or less

similar, reinforcing the prediction of the concentration

of nutrients within the sea ice released in the coastal

zone waters during the spring break-up.

2. Sampling site, material and methods

2.1. Sampling site and ice conditions

The study area in Adelie Land is close to the

continent and to the Astrolabe Glacier (Fig. 1); the

Fig. 2. Sea ice spatial distribution and change during ice break-up (1st Nov

Station (Adelie Land).

sampling site was the same as during the 1995 study

site (R1, 66839V.477 Lat., 140800V.500 Long., Fig. 1;

20 m deep). The land-fast ice is annual and never

thicker than 1.50 m, lasting from March until

December–January, but with large inter-annual varia-

tions. During 1999, the break-up at coast occurred on

5th December, while a large part of the offshore edge

of land-fast ice was broken a few weeks prior, as

illustrated by the satellite images (Fig. 2). The solid

ice thickness deceased slowly and regularly from

around 1.40 to 1.00 m (not illustrated), whereas the

platelet ice layer, less than 20 cm thick, remained

present in the same thickness during the study period

(4th November to 5th December).

The description of the land-fast ice, the position of

the coloured layer (on the back part of the bottom ice

and in the PLI) and the associated microalgal

communities were presented in detail for spring

1995 (Riaux-Gobin et al., 2000b; Riaux-Gobin et

al., 2003). In this paper, we include only preliminary

observations from microscopy analysis from samples

ember until 4th December). Black arrows indicate Dumont d’Urville


at Adelie Land; the assemblages and time successions

specific to the spring 1999 will be presented

separately. In the present paper, we used the same

abbreviated names for the different ice layers and

water masses sampled as previously used.

2.2. Sample collection and chemical parameters

The time-series was conducted in area ofF60 m2 to

minimize the impact of spatial heterogeneity of the ice.

Ice samples were collected using a motorized SIPRE

corer (Medlin and Priddle, 1990). The diameter of the

ice cores was 7.5 cm. At each sampling, two or three

cores were taken spaced 30–50 cm from each other; one

core was used for nutrient measurement and another

was for taxonomy and biomass. After measuring its

length, each core was stored in a dark plastic bag. From

each core, 10-cm slices were cut from the snow, solid

ice surface, middle and bottom ice layers. This study

only reports on the bottom-ice layer corresponding to

the solid granular ice containing the bulk of microalgal

biomass (as well as the platelet ice-like layer) and

which occurred as a brownish layer at the bottom of the

core (1–3 cm thick). Occasionally, we additionally

sampled two or three more cores specifically to study

the b3 cm bottom iceQ level. Following the removal of

the ice core, the PLI was rapidly sampled from the core

hole and stored in plastic containers; the thickness of

the PLI was estimated when scooping out from the core

hole. This layer was present in 1995 as well in 2001

(personal observation). Although the environmental

conditions suggest that this PLI layer originated from

the platelet ice, it was composed of soft millimeter

crystals and not of plate-like crystals (Riaux-Gobin et

al., 2000b). After removing the remaining crystals of

the PLI, we sampled the immediate under-ice water

(UIW) with 2-l glass bottles. From 18th November

until 5th December, the under-ice water at 5 m was also

sampled with a simplified system (PVC cylinder,

weighted, open from the surface and rapidly lift

through the core hole). These water samples, although

somewhat contaminated by some remaining PLI

crystals, are more representative of the underlying

seawater (not illustrated).

To follow the time variations occurring in the ice

during the last weeks preceding the break-up, we

sampled the ice, PLI and under-ice water at station R1

daily at mid-day when possible. Twenty-six samples

from the 4th November (Day 1) were collected over

33 days.

To confirm the coast to offshore gradient as

observed in 1995, in early November 1999, we

sampled at 4 km (OS1) and 20 km offshore (OS2),

measuring the same parameters as for the time-series.

At OS2, the snow cover was 80 cm deep, and the sea

ice thickness was 2 m.

Bottom ice, PLI, under-ice water samples were

collected and immediately frozen at �20 8C for later

nutrients analyses. Six months later at Brest (IUEM),

the samples were melted and filtered; nitrate, nitrite,

phosphate and silicic acid concentrations were meas-

ured using methods described by Treguer and Le

Corre (1975); results were expressed per unit liquid

(AM). Salinity was measured with a refractometer and

salinity results were corrected on the basis of some

deep-frozen samples (from sea ice to seawater) that

were measured later in salinity with a salinometer

(IUEM, Brest). NH4+ was measured at Adelie Land,

following Koroleff’s (1969, 1976) method with gentle

melting of samples in the dark at 4–7 8C and with

only the most microphyte enriched samples being

filtered (20 Am sieve). Analysis was undertaken in

replicate throughout. For pigment analysis, UIW

samples were filtered 1 or 2 h after sampling, onto

GF/F filters. PLI and bottom-ice samples (melted in

the dark at 4–7 8C) were also filtered, after complete

melting (from a few hours for PLI to 12–16 h for the

bottom ice) onto GF/F filters. The filters were frozen

(�20 8C) until further analysis six months later at the

LOB (Banyuls/mer). Chloropigments were extracted

in acetone and measured using spectrofluorometry

(Neveux and Lantoine, 1993).

Meteorological and satellite data (Figs. 2 and 3)

were provided by the meteorological team at Dumont

d’Urville Station (Meteo France and MeteoSat),

whereas the tidal data and bottom seawater temper-

ature were provided by ROSAME team (LEGOS/

CRGS Toulouse, France).

3. Results

3.1. Climatic conditions

Whereas in November, a large offshore bay was

open in the fast ice North of Adelie Land (Fig. 2),

Fig. 3. Hydroclimatology during the study period (barometric pressure, air temperature, tidal height and bottom seawater temperature).


closer to the continent (10–20 km), the ice break-up

started on 26th November (icebergs began to move

offshore), and coastal break-up took place on 5th

December, at night, while the ice was still 1 m thick at

R1. Several processes contributed to the ice break-up.

The mean bottom seawater temperature (at 7 m; Fig.

3) was �1.7 8C at R1 until mid November, it sharply

increased 3–4 days before the coastal break-up, and

reached �1.2 8C 41 days later. This warming period

corresponded to the initial presence of offshore

seawater free of ice. The mean air temperature

progressively, and more or less regularly, increased

from �14 8C in early November to �5.8C during the

break-up (Fig. 3). The barometric pressure decreased

from 11th November to 5th December, whereas strong

catabatic wind took place from 22nd to 25th


November and also from 3rd and 4th December (up to

137 km/h), along with strong swell that significantly

modified the sea ice extent. During the study period,

the tidal range was maximal, from 22nd to 25th

November, probably helping to weaken the ice. All

these processes were in favour of the break-up that

took place on 5th December night.

3.2. Ice conditions

At station R1 the mean ice depth varied from 147

cm on Day 1 (4th November), to 105 cm at Julian Day

33 (5th December, before break-up). Taking into

account the spatial heterogeneity of the ice sheet, the

melting was regular over time (not illustrated). If the

conditions of the break-up were completely different

from those of 1995 (and also 2001; personal

observation), the ice, platelet ice structure and snow

cover at the coast were similar from one year to

another; the land-fast ice was composed of columnar

ice with no infiltration level, and the bottom ice was

composed of 1–5 cm of granular ice, often coloured

deep brown by microalgae. The solid bottom ice layer

was always very distinct from the unconsolidated PLI

layer. While the ice was melting, the coloured bottom

ice layer became thinner, loosely connected and

brittle. At the same time, the PLI became more and

Table 1

Comparison between the b10 cm bottom ice layerQ and the b3 cm bottom

Julian

Day

Layer

(cm)

S x Chl a

Agl�1

PO4�

AM

7 10 6.62 966 10.06

7 3 16.42 nd nd

8 10 7.11 993 9.86

8 3 8.58 nd nd

9 10 7.60 1538 10.16

9 3 14.46 nd nd

11 10 5.15 1297 11.19

11 3 10.05 nd nd

12 10 5.64 1875 17.61

12 3 12.50 2897 15.75

21 10 3.68 981 10.95

21 3 5.64 3097 23.94

26 10 5.64 186 4.47

26 3 8.58 1302 23.99

29 10 5.64 359 11.49

29 3 8.58 1302 24.82

33 10 3.19 134 5.28

33 3 3.68 678 nd

more coloured. The PLI layer was thinner than in

1995 (mean 10–20 cm in 1999 versus 10–30 cm in

1995), and less coloured, except at the end of the

time-series. As in 1995, the snow cover was thin (0–5

cm, exceptionally 10 cm).

At station OS2, the snow cover was 80 cm and the

ice was 2 m thick, but as observed at station R1, the

ice column was composed of prismatic ice, with no

infiltration layer. The bottom granular ice was colour-

less, the PLI was abundant and also colourless.

3.3. Sympagic assemblages

In 1999, the deeply coloured level was located in

the bottom ice, whereas the PLI was significantly

coloured only some days before the break-up. In

1995, the deeply coloured level was noticeable in the

PLI, but the samplings late in November (15th

November) and the hydrological and meteorological

conditions were different from those of 1999. This

deeply coloured bottom ice level was 2–3 cm thick in

early November and decreased to a few millimeters

thick, as a brittle and loosely connected layer, a few

days before the break-up. The environmental con-

ditions seem to deeply influence the ecology of the ice

microalgae assemblages. In situ preliminary micro-

scopy observations showed that Navicula glaciei was

ice layerQ (nd=no data)

Si(OH)4AM

NO3�

AMNO2

�

AMNH4

+

AM

24.7 52.55 0.07 4.71

nd nd nd nd

22.24 56.10 0.12 4.17

nd nd nd nd

20.19 36.80 0.07 nd

nd nd nd nd

19.47 38.70 0.09 2.25

nd nd nd nd

21.35 39.46 0.38 2.4

15.75 58.69 0.12 4.45

18.59 26.29 0.07 2.6

51.38 38.25 0.08 11.19

11.39 0.165 0.01 2.15

11.36 13.59 0.06 4

10.66 2.05 0 1.8

14.8 0 0 0.1

11.35 8.46 0.05 4.6

19.31 nd 0.10 0


less abundant in 1999 than in 1995. We also noticed

large amounts of Berkeleya adeliensis clumps in

bottom ice at the end of the time-series (Riaux-Gobin

et al., 2000a). Time succession within species, and

spatial repartition within the different ice levels, will

be reported elsewhere.

Fig. 4. Time-series at station R1. Sampling pattern (bottom ice, platelet

November) until Day 33 (5th December 1999).

3.4. b3 cm Bottom ice layerQ

During the 1999 time-series, the bbottom ice

layerQ sampled was 10 cm thick, but the brown

layer proper was less than 3–5 cm. So, the brown

layer was in reality enriched if compared with the

ice, and under ice water). Chl a and Phaeo a, from Day 1 (4th


10 cm layer analyzed. To quantify this under-

estimate of concentration in pigments and nutrients

of the brown layer itself, for selected samples we

studied in detail the b3 cm bottom ice layerQ(Table 1).

Fig. 5. Time-series at station R1. Salinity, PO4� and Si(OH)4, from

Although five samplings of the b3 cm bottom ice

layerQ (performed in parallel to the b10 cm bottom ice

layerQ) were insufficient to account correctly for the

time variability (Table 1, not illustrated), they show

that the salinity was always higher in the b3 cm layerQ

Day 1 (4th November) until Day 33 (5th December 1999).


and decreased with time, this was also true for the

pigments (chlorophyll a [Chl a], up to 3 mg l�1 at

Day 21). The PO4� concentrations were also higher in

the b3 cm layerQ and decreased with time. For other

parameters, the differences between the b10 cm layerQand the b3 cm layerQ were less marked.

Fig. 6. Time-series at station R1. NH4+, NO3

++NO2� and NO2

�, from

3.5. Time-series

Figs. 4–7 illustrate the variations versus time, at

R1, of the chemical and biological parameters, within

the three major compartments: bottom ice (10 cm),

PLI and Under Ice Water just under the ice (UIW).

Day 1 (4th November) until Day 33 (5th December 1999).

Fig. 7. Time-series at station R1. N/P, N/Si, from Day 1 (4th November) until Day 33 (5th December 1999).


The biogeochemical variability of the UIW at 5 m,

and at other levels in the ice core is commented on but

not illustrated. In Figs. 4–7, we do not take into

account the slow decrease in the ice sheet thickness.

A clear decrease in salinity during the last 5 days

is noticeable before the break-up, affecting all layers

(ice and seawater; Fig. 5). Chl a exhibits very high

concentrations in bottom ice, until Day 24, followed

by a clear decrease, in parallel with a clear increase

in PLI. The concentrations in Phaeo a were low in

the bottom ice during the whole study period,

whereas they tended to increase vs. time in PLI.

High concentrations of ammonium were measured in

the every ice component (Fig. 6). The high NH4+

concentrations in bottom ice slightly decreased after

Day 22, whereas they increased in the PLI and UIW

at the same time. NO2� concentrations were low

concentrations in the bottom ice, a clear increase was

noticeable in PLI and UIW, but no clear increase in

UIW 5 m. Nitrate concentrations were high in the

bottom ice, from Day 5 to 15, followed by a more or

less clear increase in the PLI and UIW, and a clear

increase in UIW 5 m. PO4� showed quite similar

variations to those of Chl a (Figs. 4 and 5). Silicic

acid concentrations were low in bottom ice, suggest-

ing biological depletion (Fig. 5; also illustrated in

Fig. 9), increased slightly in PLI with time, and

showed a very clear increase in UIW and UIW 5 m

from Day 10 to 15 until break-up. The N/P ratio

decreased regularly with time in the bottom ice and

PLI, showing more irregular variations in UIW,

whereas N/Si ratio exhibits irregular variations, but

with a slight decrease in all layers, the days before

break-up.

Fig. 8. Si(OH)4 vs. PO4� concentrations of bottom ice ( y =

0.47x+10.42; R2 = 0.19), platelet ice [PLI ( y =1.55x+10.59;

R2=0.52)], and Under Ice Water (UIW) (A); NO3� vs. Si(OH)4

concentrations of bottom ice ( y =2.27x�12.29; R2=0.52), platelet

ice and Under Ice Water ( y =0.43x+2.75; R2=0.49) (B) and NO3�

vs. PO4� in the same layers (C), during austral summer at Adelie

Land, from 4th November until 5th December 1999.

Fig. 9. Chl a (log transformed) vs. PO4� concentrations of bottom

ice ( y=49.74x+229; R2=0.27), platelet ice (PLI; y=38.24x+131

R2=0.42) and Under Ice Water (UIW) (A), and vs. Si(OH)4 o

bottom ice ( y=48.55x+31.49; R2=0.30), platelet ice [PLI ( y=

14.86x+58.05; R2=0.29)], and Under Ice Water (UIW) (B) during

austral summer at Adelie Land, from 4th November until 5th

December 1999.


3.6. Coast to offshore gradient (0, 4 and 20 km

offshore)

As first shown in 1995, a spatial gradient, from

coast to offshore, was observed (not shown here), with

high concentrations of pigments and PO4� in PLI and

bottom ice at the coastal station (R1), whereas at

offshore stations (OS1 and OS2), the concentrations

were relatively very low (OS2 bottom ice Chl a: 3.6

Ag l�1; PO4�: 0.46 AM). High concentrations in NH4

+

and NO2� were reported on the whole ice column at

R1, and a decrease was observed offshore, whereas

Si(OH)4 and NO3� were in higher concentrations in

PLI and under-ice water at all stations, with no spatial

gradient evident.

4. Discussion

As illustrated by the Si versus NO3� and PO4

�

diagrams (Fig. 8A–C) we showed for the second time

that the bottom ice biogeochemical characteristics

were different from those of the platelet ice-like layer,

confirming the suggestions of Palmisano and Sullivan

(1985) that the pathways of photosynthetic assimila-

tion of these two layers from McMurdo Sound were

different, and the observations of Gunther and Die-

ckmann (2001) on the clear differentiation between

communities in fast ice and platelet layer from

Weddell Sea. The biogeochemical differences affect-

ing the bottom ice from the PLI as well as the UIW

from Adelie Land were also noticeable with respect to

pigments (Fig. 9A–B), NO2� and NH4

+ (Fig. 6).

;

f


During the EPONTA 1995 spring study, we

suggested that nitrate might be regenerated at a higher

rate than silicic acid in the microphyte-enriched PLI

layer. During the bEPONTA 1999Q time-series,

NH4+and NO2

� were specifically studied to confirm

these assertions. NH4+ seems to be actively generated

in the bottom ice, in parallel to high pigment

biomasses, until this biomass is migrating downwards

in PLI, following the bottom ice melting. Such

regeneration of NH4+ has been demonstrated in

McMurdo Sound PLI (Arrigo et al., 1995). In Adelie

Land, NH4+ seems to be massively injected into the

under-ice water masses after the break-up. NO2�

variations also confirm that nitrification actively took

place in PLI at the end of the time-series. Nitrates

increase in the UIW 5 m, in parallel to the ice melting.

PO4� was not exhausted by sympagic algae, and seems

to be also actively regenerated in bottom ice and PLI

(as illustrated in Fig. 9A), as previously demonstrated

by Arrigo et al. (1995). Gunther et al. (1999) also

observed such high PO4� concentrations in the PLI of

Drescher Inlet (Weddell Sea), and proposed a new

pathway of nutrient recycling, by way of a bliberationQafter the nitrate-based bnewQ production decay and

grazing. To ascertain within bregenerationQ or

bliberationQ processes are involved at Adelie Land,

we will focus further investigations on sea ice bacteria

and bacteria–algae relationships survey (cf. Stewart

and Fritsen, 2004). Silicate at the ice–water interface

at Adelie Land are depleted by ice algae (Fig. 9B),

whereas around the break-up, the underlying water

masses (UIW and UIW 5 m) became progressively Si

enriched by the offshore water masses entering the

bay (Fig. 5).

If we postulate that only the near shore first

kilometer (but probably more) of land-fast ice is

biologically productive (mainly due to the bottom ice

in 1999), about 0.4 kmol km�1 coastal shore of NH4+,

1 kmol km�1 NO3� and 2 kmol km�1 PO4

� may be

Table 2

Differences between some characteristics of land-fast ice, in springs 1995

Year Break-up Ice thickness

at break-up

1995 end of November 60 cm

1999 5th December 110 cm

inputted in the coastal zone waters at the break-up,

whereas 0.12 tons km�1 Chl a, equivalent to 9.6 tons

POC km�1 coastal shore (if we assume a ratio C/Chl a

of 30; cf. Palmisano and Sullivan, 1983; Arrigo et al.,

1995) were also exported downward through fast

sedimentation (Table 2). The bulk of exported

nutrients can be available for the open water spring

bloom, and the exported particulate matter can

contribute to feed the flourishing benthos of the

coastal and continental shelf zone. Sediment trap

experiments (carried out during bEPONTA 2001Q andin future projects) will give more information on the

quantitative and qualitative characteristics of the

exported particulate matter, and the exact mode of

export (bmass sedimentationQ or role of the currents intransporting this biomass).

The amount of nutrients released and the scatter-

ing/sedimentation/export microalgae during spring

break-up shows significant variation. In spring 1995,

the ice sheet was thinner and the PLI actively

colonized by ice algae; the nutrients were in higher

concentrations compared to our 1999 study. The

potential nutrient release, therefore, in the coastal

zone waters at the break-up was much higher.

With regard to the sympagic biomass and assemb-

lages in bottom ice and PLI, some inter-annual

differences were apparent. During spring 1995, the

deeply coloured layer was localized in the PLI and

was composed of a high concentration of algae,

whereas the bottom ice was less coloured with a lower

algal concentration. Some differences also were

observed between the assemblages of PLI and bottom

ice (Riaux-Gobin et al., 2003). We suggest that

colonization was not simultaneous, and that the PLI

was not only a bskeletal residueQ of the melting

bottom ice, but a specific ice level, with his own

history (cf. Gunther and Dieckmann, 2001). The sea

ice was thinner at station R1 in 1995 (80 cm on 15th

November to 60 cm on 26th November). The solar

and 1999, at station R1

Chl a max

level

NO3� max

level

Si(OH)4 max

level

9 mg l�1 300 AM 100 AMPLI PLI PLI

1.8 mg l�1 50 AM 20 AMBottom ice Bottom ice Bottom ice


irradiation cumulated period in November was very

high (433 h) and the global solar irradiation reached

82746 J/cm2. The daily maximal temperatures were

above 0 8C during 6 days in November, and small

polynya and briversQ opened at the same time.

During spring 1999, the deeply coloured level was

localized in the bottom ice; in contrast, the PLI was

colourless in early November and only brownish

some days before the break-up. The thickness of the

ice was 147 cm (in early November), 115 cm on 16th

November and still 105 cm at break-up on 5th

December. So, the ice sheet was much thicker than

in 1995. The solar irradiation cumulated period in

November was only 349 h and the global solar

irradiation reached 77697 J/cm2; the daily maximal

temperatures were positive during only 3 days in

November, and the last decade was under the mean

(mean over the previous 10 years). At the same time,

high tidal range, low barometric conditions and

significant swell occurred. All these factors favoured

break-up, despite the thickness of the ice. The greater

thickness of the ice probably resulted from low

temperature periods in the winter. This consequently

decreased the solar irradiation reaching the PLI, and

also reduced PLI colonization by ice algae in 1999.

This pairing of a colourless PLI layer with the bottom

ice that was deeply colonized favours the hypothesis

of a different origin and evolution of communities

within PLI and bottom ice (cf., Figs. 8 and 9).

In conclusion, the environmental conditions pre-

vailing during the months before the ice break-up

might significantly influence the conditions of colo-

nization in the different ice levels, and induce differ-

ences in melting and break-up conditions, from one

year to another. The land-fast ice, located in the

vicinity of Dumont d’Urville basis, shows some

reproducible features: this annual ice is less than 2

m thick and does not have intercalary coloured layers,

but present a bottom granular ice layer. This bottom

granular ice presents a coloured layer at the coast

(around 2–3 km wide, more or less thick, and showing

time variations). A platelet ice-like layer, never thicker

than 20 cm at the coast, but more than 40 cm offshore

is also present. At the coast, it may or may not be

coloured; this varies temporally and as a function of

climate. The colonization by sympagic algae of the

different components of the sea ice, particularly the

bottom ice and platelet ice, seems to be linked to

climatic and hydrographic conditions (cf Ackley and

Sullivan, 1994; Arrigo, 2003). These physical ice

features, which show relatively reproducible patterns

of nutrient distribution in the different ice layers and

under-ice water (but with concentrations depending

on the ice formation and thickness, and in great part

related to the presence of ice algae), release nutrients

and ice algae in such Antarctic coastal zone waters, at

the spring break-up, thus impacting both the open

ocean and bottom communities.

Acknowledgments

We thank the over-wintering team members for

their field assistance and fellowship during bEPONTA99Q research program. Thanks are also due to the

bAstrolabeQ polar ship crew. Thanks are due to the

Service d’Observation ROSAME (Laboratoire

d’Etudes en Geophysique et Oceanographie Spatiales;

LEGOS/CRGS Toulouse, F), for the tidal data, and

the meteorological team at Dumont d’Urville Station

(Meteo France) for their collaboration. Thanks are

also due to Dr. Amy Leventer, Dr. Michael P. Lizotte

and Dr. Carole Llewellyn for the critical review of the

manuscript, amendments and corrections. Funds and

logistic assistance on field were supported by the

Institut Polaire Francais, Paul-Emile Victor (IPEV)

formerly the bInstitut Francais pour la Recherche et laTechnologie PolairesQ (IFRTP).

References

Ackley, S.F., Sullivan, C.W., 1994. Physical controls on the

development and characteristics of Antarctic sea ice biological

communities—a review and synthesis. Deep-Sea Research 41,

1583–1604.

Arrigo, K.R., 2003. Primary production in sea ice. In: Thomas,

D.N., Dieckmann, G.S. (Eds.), Sea Ice, An Introduction to Its

Physics, Chemistry, Biology and Geology. Blackwell Science,

Oxford, pp. 143–183.

Arrigo, K.R., Robinson, D.H., Sullivan, C.W., 1993. A high

resolution study of the platelet ice ecosystem in McMurdo

Sound, Antarctica: photosynthetic and bio-optical characteristics

of a dense microalgal bloom. Marine Ecology. Progress Series

98, 173–185.

Arrigo, K.R., Dieckmann, G., Gosselin, M., Robinson, D.H., Fritsen,

C.H., Sullivan, C.W., 1995. High resolution study of the platelet

ice ecosystem in McMurdo Sound, Antarctica: biomass, nutrient,


and production profiles within a dense microalgal bloom. Marine

Ecology. Progress Series 127, 255–268.

Fiala, M., Delille, D., 1992. Variability and interactions of

phytoplankton and bacterioplankton in the Antarctic neritic

area. Marine Ecology. Progress Series 89, 135–146.

Gqnther, S., Dieckmann, G.S., 2001. Vertical zonation and

community transition of sea-ice diatoms in fast ice and platelet

layer, Weddell Sea, Antarctica. Annals of Geology 33, 287–296.

Gqnther, S., Gleitz, M., Dieckmann, G.S., 1999. Biogeochemistry of

antarctic sea ice: a case study on platelet ice layers at Drescher

Inlet, Weddell Sea. Marine Ecology. Progress Series 177, 1–13.

Koroleff, F., 1969. Direct determination of ammonia in natural

waters as indophenol blue. ICES, C.M.1969/C: 9 Hydr. Comm.

Koroleff, F., 1976. Determination of ammonia. In: K. Grasshoff, K.,

Editor, 1976. Methods of sea water analysis, Verlag Chemie,

RFA, Weinheim, pp. 126–133.

Leventer, A., 2003. Particulate flux from sea ice in polar waters. In:

Thomas, D.N., Dieckmann, G.S. (Eds.), Sea Ice, An Introduc-

tion to Its Physics, Chemistry, Biology and Geology. Blackwell

Science, Oxford, pp. 303–332.

Matsuda, O., Ishikawa, S., Kawaguchi, K., 1990. Seasonal variation

of particulate organic matter under the Antarctic fast ice and its

importance to benthic life. In: Kerry, K.R., Hempel, G. (Eds.),

Antarctic Ecosystems: Ecological Change and Conservation.

Springer-Verlag, Berlin, pp. 145–148.

McMinn, A., 1996. Preliminary investigation of the contribution of

fast-ice algae to the spring phytoplankton bloom in Ellis Fjord,

eastern Antarctica. Polar Biology 16, 301–307.

McMinn, A., Ashworth, C., Ryan, K.G., 2000. In situ net primary

productivity of an Antarctic fast ice bottom algal community.

Aquatic Microbial Ecology 21, 177–185.

Medlin, L.K., Priddle, J., 1990. Polar marine diatoms. British

Antarctic Survey, Cambridge, University Press, Cambridge,

214 pp.

Neveux, J., Lantoine, F., 1993. Spectrofluorometric assay of

chlorophylls and phaeopigments using the least squares

approximation technique. Deep-Sea Research 40, 1747–1765.

Palmisano, A.C., Sullivan, C.W., 1983. Sea ice microbial commun-

ities (SIMCO): 1. Distribution, abundance, and primary

production of ice microalgae in McMurdo Sound, Antarctica

in 1980. Polar Biology 2, 171–177.

Palmisano, A.C., Sullivan, C.W., 1985. Pathways of photosynthetic

carbon assimilation in sea-ice microalgae from McMurdo Sound

Antartica. Limnology and Oceanography 30, 674–678.

Riaux-Gobin, C., Poulin, M., Maria, E., 2000a. Role des fortes

concentrations en diatomees epontiques dans la dissociation du

cycle de l’azote et de la silice en zone cotiere antarctique et

evolution lors de la debacle. Rapport de fin de mission a Terre

Adelie (EPONTA 99-2000), IPEV, 6 pp.

Riaux-Gobin, C., Treguer, P., Poulin, M., Vetion, G., 2000b.

Nutrients, algal biomass and communities in land-fast ice and

seawater off Adelie Land (Antarctica). Antarctic Science 12,

160–171.

Riaux-Gobin, C., Poulin, M., Prodon, R., Treguer, P., 2003. Land-

fast ice microalgal and phytoplanktonic communities (Adelie

Land, Antarctica) in relation to environmental factors during ice

break-up. Antarctic Science 15 (3), 354–364.

Stewart, F.J., Fritsen, C.H., 2004. Bacteria–algae relationships in

Antarctica sea ice. Antarctic Science 16, 143–156.

Sullivan, C., Palmisano, A.C., Kottmeier, S.T., Moe, R., 1982.

Development of the sea ice microbial community in McMurdo

Sound. Antarctic Journal of the United States 17, 155–157.

Thomas, D.N., Kennedy, H., Kattner, G., Gerdes, D., Gough, C.,

Dieckmann, G.S., 2001. Biochemistry of platelet ice: its

influence on particle flux under fast ice in the Weddell Sea,

Antarctica. Polar Biology 24, 486–496.

Thomas, D.N., Papadimitriou, S., 2003. Biogeochemistry of sea ice.

In: Thomas, D.N., Dieckmann, G.S. (Eds.), Sea Ice, An

Introduction to Its Physics, Chemistry, Biology and Geology.

Blackwell Science, Oxford, pp. 267–302.

Treguer, P., Le Corre, P., 1975. Manuel d’analyses automatiques

des sels nutritifs dans l’eau de mer. Utilisation de l’Auto-

Analyzer II Technicon. Universite Bretagne Occidentale, Brest.

150 pp. (Unpublished).

land-fast ice off adélie land (antarctica): short-term variations in nutrients and chlorophyll just...

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