Historical And Modern Deep-Sea Transmissometry Data In World Ocean Database - Its Status, Challenges, And Utilization.

The World Ocean Database (WOD) contains over 13 million profiles of major oceanographic variables (T, S, etc.) with new data added continually, and is available without restriction. A subset of more than 24000 profiles include data from deep-sea transmissometers (Tr), instruments that measure the attenuation of a beam of red light (c) over a fixed path length (typically 25cm). Full water column Tr data collected along with standard hydrographic data can be applied to a variety of important scientific questions, e.g., why and how does primary production biomass change in the euphotic zone on decadal time scales? can sources of natural bottom nepheloid layers of resuspended sediment be differentiated from `industrial' sources due from future deep-sea mining? what is the role of resuspended sediment in the biogeochemical cycles of trace elements in the deep sea? Tr measurements were made over the past four decades during 550 cruises throughout all the world's ocean basins. We present a synopsis of these optical data collected during international, global programs such as the WOCE, JGOFS, and CLIVAR. Some of the transects were repeated two-three times over 10-15 years, purposely to allow an assessment of the variability of hydrographic conditions on decadal time scales. The optical measurements (c due to water and particles) throughout the entire water column made over recent decades along with the hydrographic data allow us to understand how optical conditions might be affected by climate change. Tr data have also been collected in many regional programs, e.g. SAVE in the late 1980's, and AMT beginning in the mid-1990's and continuing to today. Tr data held in WOD has been acquired using different instruments by different research teams and this brings some challenges to data post-processing and comparison. The majority of data now in WOD has been post-processed by our team, but incomplete metadata and methodology documentation have added to the difficulty of mining the historical data. New data collected by ongoing programs such as CLIVAR and GEOTRACES are being post-processed and coming to WOD on a regular basis. We encourage others who are making hydrographic measurements to include Tr measurements and submit data to WOD along with complete metadata / methodology to maximize the use of these valuable measurements.