کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4536536 1626446 2013 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Revisiting N2 fixation in the North Atlantic Ocean: Significance of deviations from the Redfield Ratio, atmospheric deposition and climate variability
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات زمین شناسی
پیش نمایش صفحه اول مقاله
Revisiting N2 fixation in the North Atlantic Ocean: Significance of deviations from the Redfield Ratio, atmospheric deposition and climate variability
چکیده انگلیسی

The average oceanic nitrate-to-phosphate molar ratio (NO3−:PO43−≈16:1, referred to as the Redfield Ratio) in subsurface waters, which is similar to the average ratio of particulate nitrogen (N)-to-phosphorus (P) in phytoplankton, is the cornerstone in calculating geochemical estimates of N2 fixation and denitrification rates. Any deviations from this canonical Redfield Ratio in intermediate ocean waters, expressed as N* (a measure of NO3− in excess or deficit of 16×PO43−), provides an integrated estimate of net N fluxes into and out of the ocean. In well-oxygenated ocean basins such as the North Atlantic Ocean, N* estimates are usually positive and can be used to infer that rates of N2 fixation exceed rates of denitrification. We use this approach to estimate N2 fixation over the last two decades (1988–2009) based on data collected at the Bermuda Atlantic Time-series Study (BATS) site in the North Atlantic Ocean near Bermuda. Our results indicate that interpretation of the N* tracer as an estimate of N2 fixation should be undertaken with caution, as N2 fixation is not the only process that results in a positive N* estimate. The impacts of a locally variable nitrogen-to-phosphorus ratio, relative to the fixed Redfield Ratio, in the suspended particulate matter as well as in the subsurface water nutrients and atmospheric N deposition on N* variability were examined. Furthermore, we explored the role of climate modes (i.e., North Atlantic Oscillation and Arctic Oscillation) on N* variability. We found that N* in the subsurface waters was significantly affected by these factors and hence previous estimates of N2 fixation using this technique might have been substantially overestimated. Our revised estimate of N2 fixation in the North Atlantic Ocean (0°N–50°N, 20°W–80°W) is 12.2±0.9×1011 mol N yr−1, and based on long-term BATS data provides better constraints than both earlier indirect and direct estimates N2 fixation.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Deep Sea Research Part II: Topical Studies in Oceanography - Volume 93, September 2013, Pages 148–158
نویسندگان
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