seaglider observations during summer...

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Seaglider Observations During Summer 2000

C. C. Eriksen1, R. D. Light2, T. W. Lehman1, T. Wen2, M. J. Perry3, A. M. Chiodi1, P. L. Sabin2,M. L. Welch2, and N. M. Bogue1

1School of Oceanography, University of Washington, Box 357940, Seattle WA 98195-79402Applied Physics Laboratory, University of Washington, Box 355640, Seattle WA 98195-5643School of Marine Science, University of Maine, Darling Marine Ctr., Walpole ME 04573-33

Summary

Two major field deployments of Seagliders took place during summer 2000, a one-msingle glider mission in Possession Sound, Washington, and a 3-glider mission in MontereyCalifornia. Over 1500 dive cycles were made in these demonstration experiments. All data aas commands to the vehicles were telemetered via cellular telephone in near real time to anremote fixed and mobile computers both ashore and aboard small vessels.

Seaglider #003 in Possession Sound was operated mostly in ‘virtual mooring’ modemaintaining its position near 3 different targets in succession (Figure 1) from 21 June throuJuly 2000. In addition to holding its position against depth-averaged tidal currents as strong am/s and a mean surface current of 0.5 m/s, it routinely traversed waters whose potential dediffered by more than 10 kg/m3, ranging from roughly half fresh water at the surface to water nearly oceanic salinity at depth. The ability to estimate depth-averaged current from the diffebetween dead-reckoned and over-the-ground displacements was demonstrated, as well asity to collect time series of temperature and salinity profiles under remote control (Figure 2)glider #003 glided over 200 nautical miles during its mission. Power usage confirmed thatdeployments in the deep ocean of several months duration and several thousand km rangesible.

Three Seagliders were deployed together in Monterey Bay during the last half of Au2000. Seagliders #002 and #003 repeatedly occupied a 15 km long transect across the conshelf, diving to within a few meters of the bottom or 250 m, whichever was shallower. Theseers typically stayed within a km of the track between successive targets (Figure 3) except depisodes of strong current. Each glider carried a coarse bathymetric map from which it dechow deep to dive based on position and desired course. The sequence of temperature andsections collected illustrates the development and decay of a wind-forced surface mixed la(Figure 4). Seaglider #004 was directed along a parallel transect ~10 km to the south, alonsouth rim of Monterey Canyon (Figure 5). In addition to a CTD, it carried oxygen and fluorecence sensors. Fluorescence was found to be strongest in the thermocline over the deep wthe canyon, in marked contrast to adjacent waters over the continental shelf. A possible extion is enhanced nutrient supply from mixing within the canyon.

1

e -.

Figure 1. Surface positions of Seaglider #003 in Possession Sound, Washington 21 Jun19 July 2000. Targets in the center and sides of the channel are given by open symbolsScatter about the targets in the along-channel direction is due to imperfect prediction ofcurrents by the glider navigation algorithm.

122˚ 24'W

122˚ 24'W

122˚ 22'W

122˚ 22'W

122˚ 20'W

122˚ 20'W

47˚ 53'N 47˚ 53'N

47˚ 54'N 47˚ 54'N

47˚ 55'N 47˚ 55'N

47˚ 56'N 47˚ 56'N

47˚ 57'N 47˚ 57'N

47˚ 58'N 47˚ 58'N

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Pos

sess

ion

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dbey

Isl

and

Whi

dbey

Isl

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Glider Targets:

W

C

E

Seaglider #003 21 June - 19 July 2000

2

0.

d)

Figure 2. Month-long depth-time section of temperature (color scale) and salinity (0.1psu contour interval for salinities 29 psu and higher, 1 psu otherwise) from 446 dive cyclesmade by Seaglider #003 in Possession Sound, Washington from 22 June to 19 July 200Upper panel shows depth-averaged current (blue) inferred from the difference betweenglider dead-reckoned and GPS displacements on each dive cycle and surface current (reinferred from the difference between successive GPS fixes bracketing communicationsactivity via cellular telephony. Strong salinity stratification near the surface and consistentebb (except during brief windy periods) characterize estuarine outflow driven by riverineforcing by the Skagit and Snohomish Rivers. Variations in deep temperature and salinitywith roughly fortnightly period suggest circulation and mixing linked to the spring-neaptidal cycle.

Possession Sound June 22 − July 19 2000

174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202

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Yearday 2000

Dep

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m)

29

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9

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29.5

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29.529.5

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.5

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Temperature ° C

9 9.5 10 10.5 11 11.5 12

174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202

−1

−0.5

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Flo

od C

urre

nt (

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)

0−150m Average

Surface

C E W E W Transects E W

3

at
Figure 3. Tracks of 3 Seagliders in Monterey Bay over 12.5 d depicted by two GPS fixlocations made at the sea surface between each dive cycle. Seagliders were launched various nearshore locations over the continental shelf and instructed to transit betweenwaypoint targets indicated in blue. About 0.5 d before recovery, all three were instructedto head to the target at 36°47’N, 122°01’W. Red symbols indicate buoy positions of the M1surface mooring maintained by MBARI. Depth contours are in m.
122˚ 05'W

122˚ 05'W

122˚ 00'W

122˚ 00'W

121˚ 55'W

121˚ 55'W

121˚ 50'W

121˚ 50'W

121˚ 45'W

121˚ 45'W

36˚ 35'N 36˚ 35'N

36˚ 40'N 36˚ 40'N

36˚ 45'N 36˚ 45'N

36˚ 50'N 36˚ 50'N

36˚ 55'N 36˚ 55'N

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TargetM1 Buoy

MossLanding

Monterey

Santa Cruz

Seaglider #002 0016Z 19 AUG - 1601Z 29 AUG 2000Seaglider #003 0002Z 17 AUG - 1333Z 29 AUG 2000Seaglider #004 2337Z 25 AUG - 1357Z 29 AUG 2000

4

Figure 4. Twelve 15 km long sections made from 17 to 26 August 2000 with Seagliders#002 and #003 across the continental shelf in central Monterey Bay. Positions are relativeto 36°48’N, 122°05’W in the direction of 36°51’N, 121°56’W. Temperatures (9-13.5°C)are in color overlain with salinity contours (interval 0.04 psu). The time sequence ofsections is across each row from left to right starting at the top left. Note the formation ofa surface mixed layer 30-40 m thick in the third and fourth sections (due to upwellingfavorable winds in excess of 20 kt on 19 and 20 August) followed by restratification insubsequent sections (when winds were weaker).

Seaglider #003 1420Z 17 August 2000 − 2340Z 18 August 2000

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Distance (kilometers)

De

pth

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ete

rs)

33.633.6

33.833.8 33

.8

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Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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33.6

33.8

33.8

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Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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33.8

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Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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33.8

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33.833.8

Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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33.8

33.833.8

33.8

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Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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33.8

33.833.8

33.8

Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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Temperature ° C

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33.8

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Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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33.833.8

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33.8

Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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33.8

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33.833.8

Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5


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Dep

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33.6

33.833.8

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33.8

Temperature ° C

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5

5

to

Figure 5. Lower panel: Track of Seaglider #004 over 3.5 d. It was launched near the headof Monterey Canyon and travelled toward targets along a transect near the south rim ofthe canyon befor being sent toward a target in mid-canyon for recovery. Upper panel:Flourescence (color, arbitrary units) and temperature (white contours, interval 0.2°C)mapped along 69°T bearing from 36°44’N, 122°0.67’W (indicated in the lower panel by ared star where 69°T is shoreward along the dashed cyan line). Note fluorescence ishighest in the thermocline and is strongest over water deeper than ~200m, perhaps dueincreased nutrient supply from mixing within the canyon.


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Fluorescence (counts)

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122˚ 05'W

122˚ 05'W

122˚ 00'W

122˚ 00'W

121˚ 55'W

121˚ 55'W

121˚ 50'W

121˚ 50'W

121˚ 45'W

121˚ 45'W

36˚ 45'N 36˚ 45'N

36˚ 50'N 36˚ 50'N

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Target

M1 Buoy

0 km

Moss

Landing

Seaglider #004 2337Z 25 August 2000 - 1357Z 29 August 2000

6

seaglider observations during summer...

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