

Kamykowski, D (2008). Estimating upper ocean phosphate concentrations using ARGO float temperature profiles. DEEPSEA RESEARCH PART IOCEANOGRAPHIC RESEARCH PAPERS, 55(11), 15801589. Abstract The ARGO freedrifting profiling float array, with > 3125 floats deployed between 60 degrees N and 60 degrees S latitudes at about 3 degrees resolution as of May 2008 and each float profiling through 2000 m every 10 days, provides a comprehensive fourdimensional view of temperature and salinity in the world ocean. The resulting dataset complements satellitebased sea surface temperature (SST) measurements and similarly will complement future satellitebased sea surface salinity measurements. Although plans exist to add biogeochemical sensors to future floats, cost and depth restrictions may limit comprehensive upgrades to a fraction of all floats deployed after 2008. Temperaturenutrient (TN) relationships provide a mechanism to estimate nutrient concentrations from temperature to supplement sparser nutrient concentration measurements potentially obtained using nonchemical approaches like ISUSbased nitrate. Both negative and positive aspects of applying a temperaturephosphate (TP) linear regression matrix with global coverage (70 degrees N and 70 degrees S) are examined. The TP linear regression matrix was derived by combining an existing 1 degrees latitude and longitude table of phosphate depletion temperatures (PDT) or Xintercepts with representative TP linear regression slopes derived from the GEOSECS dataset. Temperatures from datasets with associated latitude and longitude coordinates and, in some cases, measured phosphate concentrations ([PO4]) were matched with calculated TP linear regression slopes and Yintercepts in the global matrix with 1 degrees resolution using MSExcel Lookup worksheet functions to calculate TPestimated [PO4]. The mean deviation of TPestimated [PO4] < 3.0 mu M from measured [PO4] is 0.18 +/ 0.18 mu M at Hawaii (HOT) and 0.04 +/ 0.08 mu M at Bermuda (BATS) time series stations and 0.28 +/ 0.27 mu M over all considered World Ocean Circulation Experiment (WOCE) stations representing the different ocean basins. In general, TPestimated [PO4] represents measured [PO4] more accurately in the southern hemisphere than in the northern hemisphere. For the World Ocean Atlas 2005 (WOA05), a TPestimated [PO4] map based on annual statistical mean SST approximates an annual statistical mean measured [PO4] map in overall geographic pattern but less so in absolute concentration. ARGO 010 m temperature data and derived TPestimated [PO4] maps from all 2006 compare more favorably with the WOA05 annual statistical mean SST and measured [PO4] maps. For winter 2006, ARGO 010 m temperature and derived TPestimated [PO4] maps favorably compare with MODIS mean SST and derived TPestimated [PO4] maps. ARGO 3050 m and 75100 m temperatures from winter 2006 and derived TPestimated [PO4] demonstrate that the ARGO dataset provides a subsurface nutrient complement to nutrient inferences based on MODIS SST The TPestimated [PO4] approach is responsive to changing conditions since the independent variable, temperature, integrates ambient environmental variability as expressed in the vertical thermal structure at the time of the ARGO profile. TPestimated [PO4] can enhance the interpretation of developing ARGObased ecosystem applications by providing more specific estimates of nutrient availability than temperature alone. (C) 2008 Elsevier Ltd. All rights reserved. DOI: 10.1016/j.dsr.2008.05.017 ISSN: 09670637 