Title: Antarctic krill under sea ice: direct observations with an autonomous underwater vehicle
1Antarctic krill under sea icedirect
observations with an autonomous underwater
vehicle
- Andrew Brierley Paul Fernandes Mark
Brandon University of St Andrews Marine
Laboratory, The Open University - British Antarctic Survey Aberdeen
2Antarctic krill
- Keystone species in the Southern Ocean
- Harvested commercially
3Krill are associated with sea ice
4Krill are associated with sea ice
RRS Discovery
5Sea ice extent varies seasonally
February 14 1994
September 14 1994
6 and inter-annually
- Antarctic
- Circumpolar
- Wave
- 6 / 7 year period
- ENSO driven?
White and Peterson, 1996
7YEAR 1
8YEAR 2
9YEAR 3
10YEAR 4
11YEAR 5
12YEAR 6
13YEAR 7
14YEAR 8
15YEAR 9
16YEAR 10
17YEAR 11
18YEAR 12
19YEAR 13
20A response by krill to sea ice?
Hewitt and Linen Low, 2000
21Krill seem to be linked to ice, but
- Sampling difficulties prevent direct observations
22Krill seem to be linked to ice, but
- Sampling difficulties prevent direct observations
Divers have limited range
23Krill seem to be linked to ice, but
- Sampling difficulties prevent direct observations
Divers have limited range
Ships are disruptive
24Krill seem to be linked to ice, but
- Sampling difficulties prevent direct observations
- Evidence is circumstantial
Divers have limited range
Ships are disruptive
25Autosub new sampling technology
- Autonomous Underwater Vehicle
- 7 m 1 m
- Unmanned
- 1,600 m depth capability
- 3.5 knots speed
- 40 hours
- 260 km
- Designed and built in the UK by NERC
- Battery powered
- Pre-programmable
26The USIPS Project
We equipped Autosub with a scientific echosounder
and made the first broad-scale, direct
observations of krill under sea ice
27Marginal Ice Zone, 2001
28(No Transcript)
29The Survey
- 7 Missions
- 210 km under ice
- Autosub deployed in open water from RRS
James Clark Ross and surveyed in to ice-covered
zone (max. 27 km under ice) - Ship surveyed adjacent open water
30Survey Grid
31(No Transcript)
32Acoustic observations of krill
under sea ice
33Distribution of krill swarms
34Krill Under Ice c.f. Open Water
35Krill distribution and ice concentration
ANOVA P lt 0.0001 r2 0.85
36Conclusions
- Direct link between krill distribution and sea
ice cover observed for the first time - These observations would not have been possible
without Autosub - Krill are concentrated just inside the ice edge
an example of risk balancing? - Reductions in sea ice area may have less grave
consequences for krill than previously assumed .
3725 reduction in ice area in 1960s?
- 25 reduction in area ?
- 9 reduction in edge length
- Not a 25 reduction in habitat?
de la Mare, 1997
38Acknowledgements
- British Antarctic Survey
- Marine Laboratory, Aberdeen
- The Autosub team at Southampton Oceanography
Centre - UK Natural Environment Research Council
- Trans-Antarctic Association
- GLOBEC
39Other Data
Autosub has enable us to collect a wealth of
physical data in the Antarctic Icebergs Sea ice
thickness Illumination under sea ice
40Observations of iceberg draught
25
50
75
Depth, m
Depth, m
100
125
150
41Observations of sea ice thickness
Antarctic before Autosub
Arctic
42Large data set on sea ice thickness
Proportion, range 0 to 0.1 m
Thickness, m