Catherine Lalande

1
Estimation of the vertical export of biogenic
matter and calibration of sediment traps using
234Th in the Barents Sea

• Catherine Lalande
• Jackie Grebmeier
• Lee Cooper
• Department of Ecology and Evolutionary Biology
  University of Tennessee, Knoxville, Tennessee, USA

Brad Moran Graduate School of
Oceanography University of Rhode Island,
Narragansett, Rhode Island, USA Paul
Wassmann Norwegian College of Fishery Science,
University of Tromsø, Tromsø, Norway
2
Thorium-234 (234Th) (t 1/2 24.1
days) Naturally occurring, particle-reactive
radionuclide Tracer for scavenging processes over
time-scales of days to weeks
Uranium series
Previous studies in the Arctic Ocean to quantify
rates of scavenging and particulate organic
carbon export Bacon et al., 1989 Cochran et
al., 1995 Moran et al., 1996 and 1997 Moran
and Smith, 2000 Amiel et al., 2002 Coppola et
al., 2002 Chen et al., 2003
3
CABANERA cruise July 8-22, 2003 Carbon flux and
ecosystem feedback in the northern Barents Sea in
a era of climate change (CABANERA)

• Objectives
• Calibrate sediment traps
• Quantify particulate organic carbon (POC) export
  in the Barents Sea
• Compare the POC fluxes obtained from 234Th with
  direct POC export estimates from the drifting
  sediment traps

4
20 m
60 m
120 m
5
10m
Dissolved 234Th activity at every depth to
obtain 234Th deficit profile
20m
60m
90m
Estimate the vertical export of organic carbon
from the 234Th deficit and the POC/234Th ratio
120m
Particulate 234Th (gt53µm) POC at 20, 60 and
120m from sediment traps and pumping
20m
60m
120m
6
III
II
Activity profiles of 234Th in the Barents Sea in
July 2003
IV
I
Svalbard
Norway
Depth (m)
7
Comparison of 234Th fluxes measured by sediment
traps and pumps in the Barents Sea - July 2003
6000
5000
21
4000
11
Sediment trap 234Th flux (dpm m-2 d-1)
3000
12
2000
1000
0
0
1000
2000
3000
4000
5000
6000
Pump 234Th flux (dpm m-2 d-1)
8
Comparison of POC/Th ratios measured by sediment
traps and pumps in the Barents Sea - July 2003
100
21
80
11
60
Sediment trap POC/Th (µmol C dpm-1)
12
40
20
0
0
20
40
60
80
100
Pump POC/Th (µmol C dpm-1)
9
Comparison of POC fluxes measured by sediment
traps and pumps in the Barents Sea - July 2003
120
100
21
80
11
Sediment trap POC flux (mmol C m-2 d-1)
60
12
40
20
0
0
20
40
60
80
100
120
Pump POC flux (mmol C m-2 d-1)
10
P vs trap POC flux in the Barents Sea - July
2003
120
100
21
80
11
Trap POC flux (mmol C m-2 d-1)
60
12
40
20
0
0
20
40
60
80
100
120
P (mmol C m-2 d-1)
11
Conclusions

• Sediment traps and pump values are within a
  factor of 2 for the 2003 Barents Sea study.
• POC fluxes range between 10.8 and 33.9 mmol
  C/m2/d for the pump values and between 8.2 and
  30.5 mmol C/m2/d for the sediment traps in the
  Barents Sea in July 2003
• Additional data from Shelf-Basin Interactions
  (SBI) processes cruises in spring and summer 2004