Wei-Lei Wang

and 5 more

Marine dimethyl sulfide (DMS) is important to climate due to the ability of DMS to alter Earth’s radiation budget. However, a knowledge of the global-scale distribution, seasonal variability, and sea-to-air flux of DMS is needed in order to understand the factors controlling surface ocean DMS and its impact on climate. Here we examine the use of an artificial neural network (ANN) to extrapolate available DMS measurements to the global ocean and produce a global climatology with monthly temporal resolution. A global database of 57,810 ship-based DMS measurements in surface waters was used along with a suite of environmental parameters consisting of lat-lon coordinates, time-of-day, time-of-year, solar radiation, mixed layer depth, sea surface temperature, salinity, nitrate, phosphate, silicate, and oxygen. Linear regressions of DMS against the environmental parameters show that on a global scale mixed layer depth and solar radiation are the strongest predictors of DMS, however, they capture 14% and 12% of the raw DMS data variance, respectively. The multi-linear regression can capture more (29%) of the raw data variance, but strongly underestimates high DMS concentrations. In contrast, the ANN captures ∼61% of the raw data variance in our database. Like prior climatologies our results show a strong seasonal cycle in DMS concentration and sea-to-air flux. The highest concentrations (fluxes) occur in the high-latitude oceans during the summer. We estimate a lower global sea- to-air DMS flux (17.90±0.34 Tg S yr−1) than the prior estimate based on a map interpolation method when the same gas transfer velocity parameterization is used.

Wei-Lei Wang

and 4 more

The downward flux of organic carbon exported from the surface ocean is of great importance to the Earth’s climate because it represents the major pathway for transporting CO from the surface ocean and atmosphere into the deep ocean and sediments where it can be sequestered for a long time. Here we present global-scale estimates for the export fluxes of total, dissolved, and particulate organic carbon (TOC, DOC, and POC, respectively) constrained by observed thorium-234 (Th) activity and dissolved phosphorus (DIP) concentration in a global inverse biogeochemical model for the cycling of phosphorus and Th. We find that POC export flux is low in the subtropical oceans, indicating that a projected expansion of the subtropical gyres due to global warming will weaken the gravitational biological carbon pump. We also find that DOC export flux is low in the tropical oceans, intermediate in the upwelling Antarctic zone and subtropical south Pacific, and high in the subtropical Atlantic, subtropical north Pacific, and productive subantarctic zone (SAZ). The horizontal distribution of DOC export ratio (F/F) increases from tropical to polar regions, possibly due to the detrainment of DOC rich surface water during mixing events into subsurface waters (increasing the strength of the mixed layer pump poleward due to stronger seasonality). Large contribution to the export flux from DOC implies that the efficiency with which photosynthetically fixed carbon is exported as particles may not be as large as currently assumed by widely used global export algorithms.