Journal
GLOBAL BIOGEOCHEMICAL CYCLES
Volume 29, Issue 12, Pages 2021-2033Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2015GB005200
Keywords
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Funding
- Natural Sciences and Engineering Research Council (NSERC) of Canada
- Canadian IPY-GEOTRACES program
- University of Victoria Faculty of Graduate Studies
- NSERC USRA
- CGS-D scholarships
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During the Canada's Three Oceans and Joint Ocean Ice Study projects in the summers of 2007 and 2008, we measured particulate organic carbon to nitrogen ratios (POC:PON) throughout the euphotic zone in Subarctic and Arctic waters. Average depth-integrated values (2.65 +/- 0.19) in the Beaufort Sea and Canada Basin (BS-CB domain) were much lower than both the Redfield ratio (6.6) and the average ratios (3.9 to 5.6) measured across other Arctic-Subarctic domains. Average uptake ratios of C and N (rho C:rho N) were also lower (0.87 +/- 0.14) in BS-CB than in the other four domains (2.10 to 3.51). Decreasing POC: PON ratios were associated with low concentrations of phytoplankton C, reduced abundance of biogenic silica (bSiO(2)), a smaller relative contribution of the > 5 mu m fraction to total chlorophyll a and a larger relative contribution of small flagellates (< 8 mu m) to total phytoplankton C. In the subsurface chlorophyll a maximum (SCM) within the BS-CB domain, phytoplankton C represented only similar to 13% of POC; and therefore, the presence of heterotrophic microbes may have decreased POC: PON. These ratios are supported by data obtained during other Arctic programs in 2006, 2008, and 2009. Previous work has suggested a link between freshening of surface waters and increasing dominance of picophytoplankton and bacterioplankton in the Canada Basin, and the low POC: PON ratios measured during this study may be a consequence of this shift. Our results have ramifications for the conversion between C-and N-based estimates of primary productivity, and for biogeochemical modeling of marine Arctic waters.
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