Export production and its regulating factors in the West Antarctica Peninsula region of the Southern Ocean
Table S1: Summary of sampling time and locations, sea surface temperature, sea surface salinity, mixed layer depth, gas exchange rate, ΔO2/Ar, 17Δ,estimates of NCP, GPP and the NCP/GPP ratios, surface chlorophyll concentration, and depth-integrated phosphate and silicate drawdown. (4.589Kb)
Figure S1: Comparison of wind speed derived from NCEP/NCAR analysis with daily average “true wind” speed measured on the ship during the cruise in January 2008 and daily average wind speed measured at Palmer Station for 2000–2010. (410.6Kb)
Figure S2: Diurnal variation of Fv/Fm ratios January 2008 and the values selected by applying the raw PAR measurement window of 0–200 mV. (833.6Kb)
Figure S3: Surface phosphate concentration, surface silicate concentration, depth-integrated phosphate drawdown, and depth-integrated silicate drawdown. (5.421Mb)
Ducklow, Hugh W.
Bender, Michael L.
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KeywordSouthern Ocean; Chlorophyll; Gross primary production; Net community production; Oxygen isotopes; Phytoplankton
In connection with the Palmer LTER program, mixed layer water samples were collected during the cruise of the L.M. Gould in Jan., 2008 at 49 stations on a 20 × 100 km grid in the West Antarctica Peninsula (WAP) region of the Southern Ocean. In this study, [O2]/[Ar] ratios and the triple isotope composition of dissolved O2 were measured, and were used to estimate net community O2 production (NCP) and gross primary O2 production (GPP), respectively. These estimates are further converted to carbon export production, primary production and the f-ratio. Our measurements give NCP ranging from −3 to 76 mmol O2 m−2 day−1 (−25 to 650 mg C m−2 day−1), and GPP from 40 to 220 mmol O2 m−2 day−1 (180 to 1010 mg C m−2 day−1). The O2 NCP/GPP ratios range from −0.04 to 0.43, corresponding to f-ratios of −0.08 to 0.83. NCP and the NCP/GPP ratio are highest in the northern coastal areas, and decrease to lower values toward the southern coastal area and the open ocean. The inshore-offshore gradient appears to be regulated primarily by iron availability, as supported by the positive correlation between NCP and Fv/Fm ratios (r2 = 0.22, p < 0.05). Mixed layer depth (MLD) is inversely correlated with NCP (r2 = 0.21, p < 0.002) and NCP/GPP (r2 = 0.21, p < 0.02), and highest NCP occurred in the fresh water lenses probably formed from melted coastal glaciers. These results suggest that export production and the f-ratio increase where water stratification is intensified by input of fresh meltwater, and that mixed layer stratification is the major factor regulating NCP in the inner-shelf and coastal regions. Along-shelf variability of phytoplankton community composition is highly correlated with NCP, i.e., NCP increases when the diatom-dominated community in the south transitions to the cryptophyte-dominated one in the north. A high correlation is also observed between NCP and the logarithm of the surface chlorophyll concentration (r2 = 0.72, p < 0.0001) , which makes it possible to estimate carbon export as a function of Chl a concentration in this region.
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 26 (2012): GB2005, doi:10.1029/2010GB004028.
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