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General Session 2: Marine & estuarine biogeochemistry |
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Decadal changes of excess nitrate in the upper North Atlantic Ocean
Wednesday 11th @ 1210-1230
Conference Hall
Jin-Yu Terence Yang* , Pohang University of Science and Technology
Kitack Lee, Pohang University of Science and Technology
Il-Nam Kim, Incheon National University
Presenter Email: jinyuyang@postech.ac.kr
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| We present the spatial variation of excess nitrate (DINxs) change in the upper water column (200-500 m) of the North Atlantic (NA) over the past two decades. This analysis is based on comparison of nutrient data produced by Global Ocean Data Analysis Project Version 2 (GLODAPv2). Data indicate that DINxs generally increased in the Subtropical Mode Water (STMW) of the western NA and in the upper North Atlantic Central Water of the tropical eastern NA, indicating an increase of external N from the atmosphere (e.g. N2 fixation and N deposition). Higher rates of increase in DINxs were observed in the northwestern and southeastern NA during the recent decade, coinciding with the spatial distribution of atmospheric N deposition to the NA that generally has high fluxes over the oceans downwind of North America and Northwest Africa. This suggested that anthropogenic influence played a key role in determining the N:P stoichiometry in the NA thermocline. However, remarkable decreases in nutrient concentrations were found concurrently within the STMW, which was primarily attributable to the dilution of an enhanced STMW formation during negative phases of the North Atlantic Oscillation. Furthermore, DINxs deceased in the northeast NA over the time period, which was likely associated with a recently weakening Atlantic meridional overturning circulation leading to a reduced replenishment of N-enriched signals from subtropics. Our results highlight the significance of anthropogenic forcing and climate variability together on controlling the nutrient dynamics in the NA. |
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