Phosphorus Cycling in the Sargasso Sea: Investigation Using the Oxygen Isotopic Composition of Phosphate, Enzyme-Labeled Fluorescence, and Turnover Times

Authors

Karen McLaughlin
Jill A. Sohm
Gregory A. Cutter, Old Dominion UniversityFollow
Michael W. Lomas
Adina Paytan

Document Type

Article

Publication Date

2013

DOI

10.1002/gbc.20037

Publication Title

Global Biogeochemical Cycles

Volume

27

Issue

2

Pages

375-387

Abstract

Dissolved inorganic phosphorus (DIP) concentrations in surface water of vast areas of the ocean are extremely low (<10 nM) and phosphorus (P) availability could limit primary productivity in these regions. We explore the use of oxygen isotopic signature of dissolved phosphate (δ¹⁸O_PO4) to investigate biogeochemical cycling of P in the Sargasso Sea, Atlantic Ocean. Additional techniques for studying P dynamics including ³³P-based DIP turnover time estimates and percent of cells expressing alkaline phosphatase (AP) activity as measured by enzyme-labeling fluorescence are also used. In surface waters, δ¹⁸O_PO4 values were lower than equilibrium by 3–6%, indicative of dissolved organic phosphorous (DOP) remineralization by extracellular enzymes. An isotope mass balance model using a variety of possible combinations of enzymatic pathways and substrates indicates that DOP remineralization in the euphotic zone can account for a large proportion on P utilized by phytoplankton (as much as 82%). Relatively short DIP turnover times (4–8 h) and high expression of AP (38–77% of the cells labeled) are consistent with extensive DOP utilization and low DIP availability in the euphotic zone. In deep water where DOP utilization rates are lower, δ¹⁸O_PO4 values approach isotopic equilibrium and DIP turnover times are longer. Our data suggests that in the euphotic zone of the Sargasso Sea, DOP may be appreciably remineralized and utilized by phytoplankton and bacteria to supplement cellular requirements. A substantial fraction of photosynthesis in this region is supported by DOP uptake.

Original Publication Citation

McLaughlin, K., Sohm, J.A., Cutter, G.A., Lomas, M.W., & Paytan, A. (2013). Phosphorus cycling in the Sargasso Sea: Investigation using the oxygen isotopic composition of phosphate, enzyme-labeled fluorescence, and turnover times. Global Biogeochemical Cycles, 27(2), 375-387. doi: 10.1002/gbc.20037

Repository Citation

McLaughlin, Karen; Sohm, Jill A.; Cutter, Gregory A.; Lomas, Michael W.; and Paytan, Adina, "Phosphorus Cycling in the Sargasso Sea: Investigation Using the Oxygen Isotopic Composition of Phosphate, Enzyme-Labeled Fluorescence, and Turnover Times" (2013). OES Faculty Publications. 54.
https://digitalcommons.odu.edu/oeas_fac_pubs/54