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An assessment of upper ocean carbon and nitrogen export fluxes on the boreal continental shelf: A 3‐year study in the open Baltic Sea comparing sediment traps, 234 Th proxy, nutrient, and oxygen budgets
Author(s) -
Gustafsson Ö.,
Gelting J.,
Andersson P.,
Larsson U.,
Roos P.
Publication year - 2013
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2013.11.495
Subject(s) - continental shelf , oceanography , environmental science , sediment , sediment trap , boreal , nitrogen , temperate climate , geology , water column , chemistry , ecology , paleontology , organic chemistry , biology
Six different approaches for estimating the upper ocean export of carbon and nitrogen has been assessed using 2‐3 years of observations in the open Baltic Sea. The long‐term average export ratios, relative to primary production, were similar from approaches based on upper ocean N budget (0.29 ± 0.02), upper ocean O budget (0.25 ± 0.02), collection‐efficiency‐corrected sediment traps (0.30 ± 0.03), and 234 Th‐derived POC export (0.21 ± 0.03; POC/ 234 Th ratio from traps). Estimates of carbon export efficiency based on direct sediment traps (0.14 ± 0.02) likely reflected under trapping whereas filter‐based 234 Th‐derived POC export (0.86 ± 0.03) indicated that POC/ 234 Th ratio from filters were larger than the ratio on truly settling matter; these two approaches and estimates are thus not recommended. This study provides improved constraints on the upper ocean C and N export in offshore temperate‐boreal continental shelf regimes such as the open Baltic Proper. The long‐term export fluxes derived by averaging the four geochemically consistent yet independent approaches were for POC 44.6 ± 4.0 gC m −2 y −1 and for PON 7.0 ± 0.6 gN m −2 y −1 . This multi‐technique approach improves understanding of carbon and nitrogen cycling in the upper ocean by constraining the export efficiencies through comprehensive time‐series measurements.