High biomass, low export regimes in the Southern Ocean
Date
2006-06-28Metadata
Show full item recordCitable URI
https://hdl.handle.net/1912/1784As published
https://doi.org/10.1016/j.dsr2.2007.01.013Keyword
Ballast; Remineralization; POC; Twilight Zone; Mesopelagic; Southern Ocean; MULVFS; Opal; Carbonate; PhosphorusAbstract
This paper investigates ballasting and remineralization controls of carbon sedimentation
in the twilight zone (100-1000 m) of the Southern Ocean. Size-fractionated (<1 μm, 1-51 μm,
>51 μm) suspended particulate matter was collected by large volume in-situ filtration from the
upper 1000 m in the Subantarctic (55°S, 172°W) and Antarctic (66°S, 172°W) zones of the
Southern Ocean during the Southern Ocean Iron Experiment (SOFeX) in January-February 2002.
Particles were analyzed for major chemical constituents (POC, P, biogenic Si, CaCO3), and
digital and SEM image analyses of particles were used to aid in the interpretation of the chemical
profiles.
Twilight zone waters at 66°S in the Antarctic had a steeper decrease in POC with depth
than at 55°S in the Subantarctic, with lower POC concentrations in all size fractions at 66°S than
at 55°S, despite up to an order of magnitude higher POC in surface waters at 66°S. The decay
length scale of >51 μm POC was significantly shorter in the upper twilight zone at 66°S (δe=26
m) compared to 55°S (δe=81 m).
Particles in the carbonate-producing 55°S did not have higher excess densities than
particles from the diatom-dominated 66°S, indicating that there was no direct ballast effect that
accounted for deeper POC penetration at 55°S. An indirect ballast effect due to differences in
particle packaging and porosities cannot be ruled out, however, as aggregate porosities were high
(~97%) and variable.
Image analyses point to the importance of particle loss rates from zooplankton grazing
and remineralization as determining factors for the difference in twilight zone POC concentrations at 55°S and 66°S, with stronger and more focused shallow remineralization at
66°S. At 66°S, an abundance of large (several mm long) fecal pellets from the surface to 150 m,
and almost total removal of large aggregates by 200 m, reflected the actions of a single or few
zooplankton species capable of grazing diatoms in the euphotic zone, coupled with a more
diverse particle feeding zooplankton community immediately below.
Surface waters with high biomass levels and high proportion of biomass in the large size
fraction were associated with low particle loading at depth, with all indications implying
conditions of low export. The 66°S region exhibits this “High Biomass, Low Export” (HBLE)
condition, with very high >51 μm POC concentrations at the surface (~2.1 μM POC), but low
concentrations below 200 m (<0.07 μM POC). The 66°S region remained HBLE after iron
fertilization. Iron addition at 55°S caused a ten fold increase in >51 μm biomass concentrations
in the euphotic zone, bringing surface POC concentrations to levels found at 66°S (~3.8 μM),
and a concurrent decrease in POC concentrations below 200 m. The 55°S region, which began
with moderate levels of biomass and stronger particle export, transitioned to being HBLE after
iron fertilization. We propose that iron addition to already HBLE waters will not cause mass
sedimentation events. The stability of an iron-induced HBLE condition is unknown. Better
understanding of biological pump processes in non-HBLE Subantarctic waters is needed.
Description
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 54 (2007): 601-638, doi:10.1016/j.dsr2.2007.01.013.
Collections
Suggested Citation
Preprint: Lam, Phoebe J., Bishop, James K. B., "High biomass, low export regimes in the Southern Ocean", 2006-06-28, https://doi.org/10.1016/j.dsr2.2007.01.013, https://hdl.handle.net/1912/1784Related items
Showing items related by title, author, creator and subject.
-
Rates and mechanisms of turbulent dissipation and mixing in the Southern Ocean : results from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES)
Sheen, Katy L.; Brearley, J. Alexander; Naveira Garabato, Alberto C.; Smeed, David A.; Waterman, Stephanie N.; Ledwell, James R.; Meredith, Michael P.; St. Laurent, Louis C.; Thurnherr, Andreas M.; Toole, John M.; Watson, Andrew J. (John Wiley & Sons, 2013-06-04)The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure ... -
Southern Ocean 2001 moorings: depth and pressure vs. time from ARSV Laurence M. Gould LMG0103, LMG0201A in the Southern Ocean from 2001-2002 (SOGLOBEC project)
Beardsley, Robert C; Limeburner, Richard (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-05-18)Southern Ocean 2001 moorings: depth and pressure vs. time from ARSV Laurence M. Gould LMG0103, LMG0201A in the Southern Ocean from 2001-2002. For a complete list of measurements, refer to the full dataset description in ... -
Data collected daily along the ship track in JGOFS format from ARSV Laurence M. Gould and RVIB Nathaniel B. Palmer cruises to the Southern Ocean from 2001-2003 as part of the Southern Ocean GLOBEC project.
Beardsley, Robert C; Costa, Daniel P.; Limeburner, Richard; Torres, Joseph J.; Wiebe, Peter H. (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-03-27)Data collected daily along the ship track in JGOFS format from ARSV Laurence M. Gould and RVIB Nathaniel B. Palmer cruises to the Southern Ocean from 2001-2003 as part of the Southern Ocean GLOBEC project For a complete ...