Trull et al., JGR-Oceans, accepted for publication.
This is a deep sediment trap paper which includes 230Th-based assessments
of collection efficiency , which I include because I think that extension
of our considerations to deep traps, and to 230Th and 231Pa may be useful.
In that regard, the recent paper by Yu et al., on the use of 231Pa/230Th
ratios in the assessment of deep trap efficiency may be of interest (E.-F.
Yu et al., 2001. Trapping efficiency of bottom-tethered sediment traps
estimated from the intercepted fluxes of 230Th and 231Pa. Deep-Sea
Research, 48(3): 865-889).
Moored Sediment Trap Measurements of Carbon Export
in the Sub-Antarctic and Polar Frontal Zones
of the Southern Ocean, south of Australia.
T.W. Trull1, S.G. Bray1, S.J. Manganini2, S. Honjo2, and R. François2
1. Antarctic Cooperative Research Centre, University of Tasmania, Hobart,
2. Woods Hole Oceanographic Institution, Woods Hole, MA, U.S.A.
Revised Draft March 28, 2001
The SAZ project organized by the Antarctic CRC has a continuing program of
moored sinking particle trap studies in the Sub-Antarctic and Polar Frontal
Zones southwest of Tasmania along 140°E longitude. The first deployment
obtained weekly or higher resolution samples through the austral summer
from September 1997 through February 1998 at three locations: the central
Sub-Antarctic Zone (~47°S, traps at 1060, 2050, and 3850m depth), the
Sub-Antarctic Front (~51°S, 1 trap at 3080m) and above the Southeast Indian
Ridge in the Polar Frontal Zone (~54°S, 2 traps at 830 and 1580m).
Particle fluxes were high at all the sites (18 to 32 g m-2 yr-1 total mass
flux and 0.5 to 1.4 g organic carbon m-2 yr-1 at ~1000m depth, assuming
minimal flux outside the sampled summer period). These values are similar
to other recent Southern Ocean deep sediment trap results, and to the
median estimated for the global ocean by Lampitt and Antia (1997).
For the 153 day collection period, particulate organic carbon export was
somewhat higher in the SAZ (range 0.57 to 0.76 gC m-2 yr-1) than in the PFZ
(range 0.31 to 0.53). The fraction of surface organic carbon export
(estimated from seasonal surface water nutrient depletion) reaching 1000m
was indistinguishable in the two zones, despite considerably different
phytoplankton communities, in particular the more frequent occurrence and
greater abundance of large diatoms in the PFZ.
Pronounced seasonality was observed at all the sites. The SAZ site
exhibited similar late-spring and late-summer periods of elevated flux and
was dominated by carbonate export (>50% of total mass), while the PFZ site
exhibited higher flux in summer than spring and was dominated by biogenic
silica export (>50% of total mass) throughout the year. The spring
increase in export and late summer decrease were similar to the timing
observed by the AESOPS program near 170°W, but the presence of a low flux
period in all the SAZ project traps in December was a strong contrast.
Comparison with sea-surface height records suggests movement in frontal
positions was not a major factor in the observed SAZ and PFZ seasonal
variations, although it did affect the SAF results. The deployment year
experienced unusually cool sea surface temperatures throughout summer, and
it is possible this influenced export, although surface nutrient depletion
for the deployment year was similar to a previous year with a more typical
amplitude of surface warming. With the caveat of possibly strong
interannual variability, consideration of remote sensing and hydrographic
results suggests the SAZ project particle fluxes can be taken as
representative of the SAZ and PFZ for the East Antarctic sector of the
Southern Ocean from 90 to 145°E.