Abstract
The proportion in which carbon and growth-limiting nutrients are exported from the oceans’ productive surface layer to the deep sea is a crucial parameter in models of the biological carbon pump. Based on >400 vertical flux observations of particulate organic carbon (POC) and nitrogen (PON) from the European Arctic Ocean we show the common assumption of constant C:N stoichiometry not to be met. Exported POC:PON ratios exceeded the classical Redfield atomic ratio of 6.625 in the entire region, with the largest deviation in the deep Central Arctic Ocean. In this part the mean exported POC:PON ratio of 9.7 (a:a) implies c. 40% higher carbon export compared to Redfield-based estimates. When spatially integrated, the potential POC export in the European Arctic was 10–30% higher than suggested by calculations based on constant POC:PON ratios. We further demonstrate that the exported POC:PON ratio varies regionally in relation to nitrate-based new production over geographical scales that range from the Arctic to the subtropics, being highest in the least productive oligotrophic Central Arctic Ocean and subtropical gyres. Accounting for variations in export stoichiometry among systems of different productivity will improve the ability of models to resolve regional patterns in carbon export and, hence, the oceans’ contribution to the global carbon cycle will be predicted more accurately.
Highlights
The concept of new vs. regenerated primary production sensu Dugdale and Goering (1967) [1] has profoundly shaped the understanding of biological production and carbon sequestration in the ocean
Regional Patterns in the European Arctic Ocean The exported particulate organic carbon (POC):PON ratio increased with depth in only 8 of 61 vertical flux profiles, and comparisons are based on all observations between 20 and 200 m depth
This study shows that the C:N ratio of exported particulate organic matter is consistently above Redfield, implying that biogeochemical models based on Redfield stoichiometry underestimate POC export in the ocean
Summary
The concept of new vs. regenerated primary production sensu Dugdale and Goering (1967) [1] has profoundly shaped the understanding of biological production and carbon sequestration in the ocean. Carbon overconsumption in response to increased atmospheric CO2 is suggested to increase the spread of suboxic regions in the ocean due to respiration of excess carbon exported from the surface layer [8]. These findings suggest that our ability to predict how perturbations to the ocean environment affect the marine ecosystem in part depend on our understanding of the stoichiometric coupling between carbon and nutrients. Because nitrogen recycling within the euphotic zone varies regionally with primary production [2], export stoichiometry and, the efficiency of the biological carbon pump should reflect nutrient availability or trophic state (oligo-, meso-, eutrophy) of pelagic ecosystems
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