Shanlin Wang

Influence of explicit Phaeocystis parameterizations on the global distribution of marine dimethyl sulfide

Dimethyl sulfide (DMS) is a biogenic organosulfur compound which contributes strongly to marine aerosol mass and the determination of cloud condensation nuclei over the remote oceans. Since uncertainties in DMS flux to the atmosphere lead to large variations in climate forcing, the global DMS distribution has been the subject of increasingly complex dynamic simulations. DMS concentrations are directly controlled by marine ecosystems. Phaeocystis is a major DMS producer but is often omitted from global reduced sulfur mechanisms. Here we incorporate this phytoplankton group into the marine ecosystem-biogeochemical module of the Community Earth System Model. To examine its role in the ocean sulfur cycle, an earlier DMS model has been enhanced to include new knowledge gained over the last few years. Results from the baseline run show that simulated Phaeocystis biomass generally agrees with observations, with high concentrations near the Antarctic continent and between 50° and 60° north. Given the new explicit Phaeocystis representation, the DMS distribution shows significant improvements, especially regarding the amplitude and location of high-latitude peaks. The simulated global mean surface DMS value is 2.26 nM, comparable to an estimate of 2.34 nM from the latest climatology extrapolated based on observations. The total oceanic DMS source to the atmosphere is 20.4 Tg S/yr, on the low side of previous estimates. Comparisons with and without Phaeocystis show that the group dominates DMS distributions in temperate and cold waters, contributing 13% of the global flux. The proportion may increase as sea ice declines and should be considered in climate projections.

Global distribution and surface activity of macromolecules in offline simulations of marine organic chemistry

Organic macromolecules constitute a high percentage of remote sea spray. They enter the atmosphere through adsorption onto bubbles followed by bursting at the ocean surface, and go on to influence the chemistry of the fine mode aerosol. We present a global estimate of mixed-layer macromolecular distributions, driven by offline marine systems model output. The approach permits estimation of oceanic concentrations and bubble film surface coverages for several classes of organic compound. Mixed layer levels are computed from the output of a global ocean ecodynamics model by relating the macromolecules to standard biogeochemical tracers. Steady state is assumed for labile forms, and for longer-lived components we rely on ratios to existing transported variables. Adsorption is then represented through conventional Langmuir isotherms, with equilibria deduced from laboratory analogs. Open water concentrations locally exceed one micromolar carbon for the total of proteins, polysaccharides and refractory heteropolycondensates. The shorter-lived lipids remain confined to regions of strong biological activity. Results are evaluated against available measurements for all compound types, and agreement is generally well within an order of magnitude. Global distributions are further estimated for both fractional coverage of bubble films at the air–water interface and the two-dimensional concentration excess. Overall, we show that macromolecular mapping provides a novel tool for the comprehension of oceanic surfactant patterns. These results may prove useful in planning field experiments and assessing the potential response of surface chemical behaviors to global change.

Influence of dimethyl sulfide on the carbon cycle and biological production

Dimethyl sulfide (DMS) is a significant source of marine sulfate aerosol and plays an important role in modifying cloud properties. Fully coupled climate simulations using dynamic marine ecosystem and DMS calculations are conducted to estimate DMS fluxes under various climate scenarios and to examine the sign and strength of phytoplankton-DMS-climate feedbacks for the first time. Simulation results show small differences in the DMS production and emissions between pre-industrial and present climate scenarios, except for some areas in the Southern Ocean. There are clear changes in surface ocean DMS concentrations moving into the future, and they are attributable to changes in phytoplankton production and competition driven by complex spatially varying mechanisms. Comparisons between parallel simulations with and without DMS fluxes into the atmosphere show significant differences in marine ecosystems and physical fields. Without DMS, the missing subsequent aerosol indirect effects on clouds and radiative forcing lead to fewer clouds, more solar radiation, and a much warmer climate. Phaeocystis, a uniquely efficient organosulfur producer with a growth advantage under cooler climate states, can benefit from producing the compound through cooling effects of DMS in the climate system. Our results show a tight coupling between the sulfur and carbon cycles. The ocean carbon uptake declines without DMS emissions to the atmosphere. The analysis indicates a weak positive phytoplankton-DMS-climate feedback at the global scale, with large spatial variations driven by individual autotrophic functional groups and complex mechanisms. The sign and strength of the feedback vary with climate states and phytoplankton groups. This highlights the importance of a dynamic marine ecosystem module and the sulfur cycle mechanism in climate projections.

Effects of Model Resolution and Ocean Mixing on Forced Ice‐Ocean Physical and Biogeochemical Simulations Using Global and Regional System Models

The current coarse-resolution global Community Earth System Model (CESM) can reproduce major and large-scale patterns but is still missing some key biogeochemical features in the Arctic Ocean, e.g., low surface nutrients in the Canada Basin. We incorporated the CESM Version 1 ocean biogeochemical code into the Regional Arctic System Model (RASM) and coupled it with a sea-ice algal module to investigate model limitations. Four ice-ocean hindcast cases are compared with various observations: two in a global 18 (40 60 km in the Arctic) grid: G1deg and G1deg-OLD with/without new sea-ice processes incorporated; two on RASM’s 1/128 ( 9 km) grid R9km and R9km-NB with/without a subgrid scale brine rejection parameterization which improves ocean vertical mixing under sea ice. Higher-resolution and new sea-ice processes contributed to lower model errors in sea-ice extent, ice thickness, and ice algae. In the Bering Sea shelf, only higher resolution contributed to lower model errors in salinity, nitrate (NO3), and chlorophyll-a (Chl-a). In the Arctic Basin, model errors in mixed layer depth (MLD) were reduced 36% by brine rejection parameterization, 20% by new sea-ice processes, and 6% by higher resolution. The NO3 concentration biases were caused by both MLD bias and coarse resolution, because of excessive horizontal mixing of high NO3 from the Chukchi Sea into the Canada Basin in coarse resolution models. R9km showed improvements over G1deg on NO3, but not on Chl-a, likely due to light limitation under snow and ice cover in the Arctic Basin.

Impacts of Marine Ecodynamics on the Dimethyl Sulfide(DMS) Production

March 4 th @ noon – Jones Annex 101 Dimethyl sulfide (DMS) is a biogenic organosulfur compound which contributes strongly to marine aerosol mass and the determination of cloud condensation nuclei over the remote oceans. DMS concentrations are directly controlled by marine ecosystems. Various marine mircoorganisms play different roles in the DMS production. Changes in phytoplankton production and community composition can alter the production and distributions of DMS. Observation based estimates showed significant changes in phytoplankton biomass in the last few decades; and climate models also project a reduced marine primary production and shifts in the plankton community structure in the future climate. Here we investigate the contribution of individual phytoplankton functional groups to the DMS production and fluxes to the atmosphere using the improved marine ecosystem-biogeochemical module of the Community Earth System Model (CESM). We will examine the impacts of shifts in phytoplankton community composition on DMS distributions in a RCP climate scenario. We will show changes in the DMS flux due to individual phytoplankton groups, and the subsequent impacts on cloud radiative forcing.

Arctic Riverine CDOM and its effects on the Polar Marine Light Field

It is well-known that CDOM (Chromophoric Dissolved Organic Matter) can have a significant effect on biological activity in the photic zones of aquatic ecosystems. However, the extent of CDOM’s interference with biological activity is not well-known. We examined this issue in great detail in the mixed surface layer of the Arctic Ocean. We studied the impacts of CDOM’s light attenuation on Arctic phytoplankton populations to discover if riverine CDOM’s presence in the Arctic ocean could inhibit and possibly prevent local phytoplankton populations from performing photosynthesis. We incorporated biogeochemistry concepts and data with oceanographic models and calculations to approach the problem. The results showed that riverine CDOM can indeed significantly impact the productivity of phytoplankton populations during the spring and summer months near the major Arctic river mouths we chose to examine. Although our study was detailed and inclusive of many variables, the issue of CDOM’s light attenuation and its effects on phytoplankton populations must be explored on a global scale to help understand if riverine CDOM could prove disastrous for phytoplankton populations.