Yanyun Liu

Downscaled projections of Caribbean coral bleaching that can inform conservation planning

Abstract Projections of climate change impacts on coral reefs produced at the coarse resolution (~1°) of Global Climate Models (GCMs) have informed debate but have not helped target local management actions. Here, projections of the onset of annual coral bleaching conditions in the Caribbean under Representative Concentration Pathway (RCP) 8.5 are produced using an ensemble of 33 Coupled Model Intercomparison Project phase‐5 models and via dynamical and statistical downscaling. A high‐resolution (~11 km) regional ocean model (MOM4.1) is used for the dynamical downscaling. For statistical downscaling, sea surface temperature (SST) means and annual cycles in all the GCMs are replaced with observed data from the ~4‐km NOAA Pathfinder SST dataset. Spatial patterns in all three projections are broadly similar; the average year for the onset of annual severe bleaching is 2040–2043 for all projections. However, downscaled projections show many locations where the onset of annual severe bleaching (ASB) varies 10 or more years within a single GCM grid cell. Managers in locations where this applies (e.g., Florida, Turks and Caicos, Puerto Rico, and the Dominican Republic, among others) can identify locations that represent relative albeit temporary refugia. Both downscaled projections are different for the Bahamas compared to the GCM projections. The dynamically downscaled projections suggest an earlier onset of ASB linked to projected changes in regional currents, a feature not resolved in GCMs. This result demonstrates the value of dynamical downscaling for this application and means statistically downscaled projections have to be interpreted with caution. However, aside from west of Andros Island, the projections for the two types of downscaling are mostly aligned; projected onset of ASB is within ±10 years for 72% of the reef locations.

Wind-driven ocean dynamics impact on the contrasting sea-ice trends around West Antarctica

Since late 1978, Antarctic sea-ice extent in the East Pacific has retreated persistently over the Amundsen and Bellingshausen Seas in warm seasons, but expanded over the Ross and Amundsen Seas in cold seasons, while almost opposite seasonal trends have occurred in the Atlantic over the Weddell Sea. By using a surface-forced ocean and sea-ice coupled model, we show that regional wind-driven ocean dynamics played a key role in driving these trends. In the East Pacific, the strengthening Southern Hemisphere (SH) westerlies in the region enhanced the Ekman upwelling of warm upper Circumpolar Deep Water and increased the northward Ekman transport of cold Antarctic surface water. The associated surface ocean warming south of 68°S and the cooling north of 68°S directly contributed to the retreat of sea ice in warm seasons and the expansion in cold seasons, respectively. In the Atlantic, the poleward shifting SH westerlies in the region strengthened the northern branch of the Weddell Gyre, which in turn increased the meridional thermal gradient across it as constrained by the thermal wind balance. Ocean heat budget analysis further suggests that the strengthened northern branch of the Weddell Gyre acted as a barrier against the poleward ocean heat transport, and thus produced anomalous heat divergence within the Weddell Gyre and anomalous heat convergence north of the gyre. The associated cooling within the Weddell Gyre and the warming north of the gyre contributed to the expansion of sea ice in warm seasons and the retreat in cold seasons, respectively.

Projections of future habitat use by Atlantic bluefin tuna: mechanistic vs. correlative distribution models

mechanistic vs. correlative distribution models Barbara A. Muhling,* Richard Brill, John T. Lamkin, Mitchell A. Roffer, Sang-Ki Lee, Yanyun Liu and Frank Muller-Karger Princeton University Program in Atmospheric and Oceanic Science, Forrestal Campus/Sayre Hall, Princeton, NJ 08544, USA NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ 08540, USA James J. Howard Marine Sciences Laboratory, Northeast Fisheries Science Center, NOAA National Marine Fisheries Service, Highlands, NJ, USA Southeast Fisheries Science Center, NOAA National Marine Fisheries Service, Miami, FL 33149, USA Roffer’s Ocean Fishing Forecasting Service, Inc, West Melbourne, FL 32904, USA Atlantic Oceanographic and Meteorological Laboratory, NOAA Office of Oceanic and Atmospheric Research, Miami, FL 33149, USA University of Miami Cooperative Institute for Marine and Atmospheric Studies, Miami, FL 33149, USA College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA *Corresponding author: tel: þ1-609-452-5322; e-mail: Barbara.Muhling@noaa.gov