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Understanding the unique biogeochemistry of the Mediterranean Sea: Insights from a coupled phosphorus and nitrogen model
Author(s) -
Powley Helen R.,
Krom Michael D.,
Van Cappellen Philippe
Publication year - 2017
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2017gb005648
Subject(s) - biogeochemical cycle , biogeochemistry , oceanography , environmental science , mediterranean sea , denitrification , mediterranean climate , phosphorus , water column , reactive nitrogen , ocean gyre , nitrate , nitrogen cycle , environmental chemistry , nitrogen , chemistry , subtropics , ecology , geology , biology , organic chemistry
The Mediterranean Sea (MS) is an oligotrophic basin whose offshore water column exhibits low dissolved inorganic phosphorus (P) and nitrogen (N) concentrations, unusually high nitrate (NO 3 ) to phosphate (PO 4 ) ratios, and distinct biogeochemical differences between the Western Mediterranean Sea (WMS) and Eastern Mediterranean Sea (EMS). A new mass balance model of P and N cycling in the WMS is coupled to a pre‐existing EMS model to understand these biogeochemical features. Estimated land‐derived inputs of reactive P and N to the WMS and EMS are similar per unit surface area, but marine inputs are 4 to 5 times greater for the WMS, which helps explain the approximately 3 times higher primary productivity of the WMS. The lateral inputs of marine sourced inorganic and organic P support significant fractions of new production in the WMS and EMS, similar to subtropical gyres. The mass balance calculations imply that the MS is net heterotrophic: dissolved organic P and N entering the WMS and EMS, primarily via the Straits of Gibraltar and Sicily, are mineralized to PO 4 and NO 3 and subsequently exported out of the basin by the prevailing anti‐estuarine circulation. The high deepwater (DW) molar NO 3 :PO 4 ratios reflect the high reactive N:P ratio of inputs to the WMS and EMS, combined with low denitrification rates. The lower DW NO 3 :PO 4 ratio of the WMS (21) compared to the EMS (28) reflects lower reactive N:P ratios of inputs to the WMS, including the relatively low N:P ratio of Atlantic surface water flowing into the WMS.