OS14A-01 INVITED
Where California Meets Alaska: Ecosystem Response in a Transition Zone
Ecosystems along the west coast of Vancouver Island share features with those of the northern California Current and also with the southern part of the Alaska Coastal Current, and provide the richest fisheries of these two regimes. Studies of the past few decades reveal surprisingly consistent biological responses to changes in ocean temperatures, partly due to the extreme warm and cool years since 1998. Zooplankton populations, migrating salmon, and fledgling seabirds are rapidly affected by changing ocean conditions, whereas the biomass of resident fish stocks responds over several years or even decades. The specific mechanisms responsible for these temperature-related changes vary from species to species, and many are unknown. We will present examples of how influx of predators, timing of food availability, and wind and coastal weather contribute to the response of coastal populations. Results are based on statistical analyses of many decades of observations and also on biophysical models. The responses to past temperature variability suggest which species will eventually thrive with climate warming and the speed with which these changes might occur. One unresolved factor is the ability of cold water species to survive and rebound after warm years, and of warm-water species to recover after cold years. These responses will be increasingly important, because the IPCC models suggest increasing local ocean temperature variability during this century.
OS14A-02
Sea Surface Temperature Changes along the US East Coast over the Last 100-plus Years
Sea surface temperature variations along the entire US east coast from 1875 – 2006 are characterized using a unique collection of historical observations from lighthouses and lightships combined with recent buoy and shore-based measurements. Over the last 100 years, temperatures along the northeast US coast have warmed at a rate 2-3 times the regional atmospheric temperature trend, but comparable to warming rates for the Arctic and Labrador – the source of coastal ocean waters north of Cape Hatteras (36° N). The observations and a simple model show that along-shelf transport, associated with the mean coastal current system running from Labrador to Cape Hatteras, is the mechanism controlling long-term temperature changes for this region, and not the local air-sea exchange of heat.
OS14A-03
Seasonal and Interannual Variability in Stratification in the Gulf of Maine: Salinity and Temperature Contributions and Climatic Forcing
Seasonality and interannual variability in stratification in the Gulf of Maine impact physical processes, including the connectivity and transport of the coastal current system and isolation of surface waters. These physical processes in turn impact biological processes, such as the spring phytoplankton bloom, growth and transport of eggs and larvae of commercial species, and Harmful Algal Blooms. We use seven years of data from the Gulf of Maine Ocean Observing System (GoMOOS) to describe and explain seasonal and interannual variability in stratification. Results highlight the dominant role of salinity, particularly on the coastal shelf during spring and fall when salinity gradients increase and decrease episodically in geographically irregular and inter-annually varying patterns. As a result, short-term, large amplitude stratification events occur during some years and not others, with likely biological implications. By contrast, the vertical temperature gradients that control surface stratification during summer (June-September) display classical seasonal cycles that vary much less between years and locations. Comparison with oceanic inflows, river inflows, and meteorological data leads to a refined understanding of the relative importance of the physical mechanisms that control the hydrography, particularly salinity and stratification. These insights into seasonal and interannual variability will enhance our ability to predict the Gulf of Maine response to future changes in climatic forcing.
OS14A-04
Biomarker Evidence of Different Trends and Mechanisms of Phytoplankton Community Structure Changes in the Yellow Sea and the East China Sea During the Past 200 Years
Marine phytoplankton biomarker contents have been determined in two cores (10694 and H1-18) drilled from the southern Yellow Sea (YS) and the East China Sea (ECS) continental shelf area outside the Changjiang estuary respectively, and they are used to reconstruct phytoplankton productivity and community structure changes over the last 200 years. Our results indicate that productivity in both the YS and the ECS shelf increased during the past 100 years, especially over the last 40 years. Biomarker ratios indicate obvious changes of phytoplankton community structures but the trends are opposite in these two marginal seas. In the YS, diatom contribution increased and dinoflagellate contribution decreased during the last 100 years. However, in the ECS shelf, diatom contribution decreased and dinoflagellate contribution increased. By comparison with modern survey results, it is concluded that increases in both productivity and diatom contribution in the YS are mainly caused by strengthened Asian winter monsoon and ENSO over the last 100 years, while increases in productivity and decreases of diatom contribution in the ECS shelf are related to the enhanced nutrients input (particularly dissolved inorganic nitrogen) due to human activity. These results show that biomarkers can be used to reconstruct ecosystem variations over the last 100 years in these marginal seas, and to help partially discriminate the effects between climate change and human activity on marine ecosystem changes.
OS14A-05
Contribution of Regional Climate Drivers to Future Winter Sea-Level Changes in the Baltic Sea Estimated by Statistical Methods and Simulations of Climate Models
A statistical downscaling approach is applied to the output of different global climate model simulations driven by SRES A2 future scenarios of greenhouse gas concentrations to estimate the contribution of changes in the atmospheric circulation and in precipitation to regional future winter sea-level changes. The method is based on observed statistical relationships between Sea level as predictand and large-scale climate fields as predictors. The approach is applied to the Baltic Sea as it is one of the largest brackish seas in the world and a clear example for a complex coupled ocean-atmosphere land system with a complex coastline and bathymetry. Recent studies indicated that Baltic Sea level variations on decadal and longer time scales are strongly influenced by atmospheric forcings, but the influence of different large-scale forcing factors on sea level vary geographically. While the decadal sea level variations in the northern and eastern Baltic gauges are strongly influenced by the atmospheric circulation, the decadal variations in the southern Baltic Sea can be (statistically) better explained by area-averaged precipitation. The results indicate that future trends in sea-level rise caused by these forcing are larger than the past variability. Using sea level pressure as predictor for the central and eastern Baltic Sea level stations, three climate models lead to 21st century future trends in the range of the order of 1 to 2 mm/year. Using precipitation as predictor for the stations in the Southern Baltic Coast all five models lead to significant trends with a range of the order of 0.4 mm/year. These numbers are smaller, but of the order of magnitude as the predicted future global sea level rise. Nevertheless, these estimations comprise only a partial contribution of selected large-scale regional predictors and an estimation of the total regional sea-level rise has to consider other regional factors such as the isostatic contribution to relative sea-level changes or substantial changes in the sea-ice cover and global sea level rise.
OS14A-06
Potential climate-change impacts on the Chesapeake Bay
We review current understanding of the potential impact of climate change on the Chesapeake Bay. Scenarios for carbon dioxide emissions indicate that by the end of the 21st century the Bay region will experience significant changes in climate forcings with respect to historic conditions, including increases in carbon dioxide concentrations, sea level, and water temperature of 50-160 percent, 0.7-1.6 m, and 2-6 K, respectively. Also likely are increases in precipitation amount (particularly in the winter and spring), precipitation intensity, intensity of tropical and extratropical cyclones (though their frequency may decrease), and sea-level variability. The greatest uncertainty is associated with changes in annual streamflow, though it is likely that winter and spring flows will increase. Climate change alone will cause the Bay to function very differently in the future. Likely changes include: (1) an increase in coastal flooding and submergence of estuarine wetlands; (2) an increase in salinity variability on many time scales; (3) an increase in harmful algae; (4) an increase in hypoxia; (5) a reduction of eelgrass, the dominant submerged aquatic vegetation in the Bay; and (6) altered interactions among trophic levels, with warm-water fish and shellfish species ultimately being favored in the Bay. The magnitude of these changes is sensitive to the carbon dioxide emission trajectory, so that actions taken now to reduce carbon dioxide emissions will reduce climate impacts on the Bay. Research needs include improved precipitation and streamflow projections for the Bay watershed and whole-system monitoring and modeling (supplemented by process studies) that can capture the likely non-linear responses of the Chesapeake Bay system to climate variability and change.
OS14A-07
Nor'easter Storms and Sediment Transport Processes in Tidal Marshes of Delaware Bay
Remote and local wind forcing associated with Mid-Atlantic coastal storms has a major influence on circulation in Delaware Bay and contiguous tidal waters. In this study the role of nor'easter storms on flow and sediment transport in fringing marshes of the bay was investigated, focusing on the St. Jones River and Blackbird Creek subestuaries, Delaware National Estuarine Research Reserve (DNERR) sites. Coherence analysis of NOAA and DNERR wind data, river discharge, tidal stage, and turbidity for the period 1996-2007 indicates that northeasterly, along-shelf winds are the predominant influence on subtidal water levels and flow in the subestuaries; local winds and freshwater discharge appear to be of secondary importance. Among types of oceanic storms impacting coastal Delaware, events classified by NOAA as nor'easters consistently produce water-level and turbidity extremes. To elucidate specific mechanisms of sediment flux during fair weather and storm conditions, timeseries measurements of tidal currents, water level, and suspended sediment concentration were made at mid-channel and marsh platform locations in 2007 (St. Jones River) and 2008 (Blackbird Creek). Four nor'easters occurred during the deployment period, and the observations reveal a consistent pattern. With the onset of northeasterly coastal winds, mean tide level in the channel begins to rise. The related increase in tidal stress on the bed increases instantaneous sediment concentrations, as well as the tidally averaged total sediment flux. Specifically, the tidal pumping component of the total flux increases because settling of particles resuspended around times of peak flood and ebb flow lags the critical shear stress for deposition. The advective component of the total flux increases with rainfall runoff and produces a down-estuary flux. In contrast, wind setup near the mouth generates a comparatively larger up-estuary advective flux. Averaged over the storm period a net landward sediment flux results. Storm surge increases the hydraulic duty and hydroperiod on the adjacent marsh platform; storm hydroperiod is on average three hours longer than a typical spring tide inundation. The combination of super-elevated storm tide, extended overmarsh hydroperiod, and increased suspended load intensifies channel-to-marsh sediment delivery and deposition relative to that during fair weather spring tides. Although nor'easters cause significant erosion at the estuary inlets and adjacent barrier beaches, our observations suggest that fine sediment trapping and net accretion on the marsh platform should be augmented by these storms.
OS14A-08
Astronomical Forcing of Salt Marsh Biogeochemical Cascades
Astronomically forced changes in the hydroperiod of a salt marsh affect the rate of marsh primary production leading to a biogeochemical cascade. For example, salt marsh primary production and biogeochemical cycles in coastal salt marshes are sensitive to the 18.6-year lunar nodal cycle, which alters the tidal amplitude by about 5 cm. For marshes that are perched high in the tidal frame, a relatively small increase in tidal amplitude and flooding lowers sediment salinity and stimulates primary production. Porewater sulfide concentrations are positively correlated with tidal amplitude and vary on the same cycle as primary production. Soluble reactive phosphate and ammonium concentrations in pore water also vary on this 18.6- year cycle. Phosphate likely responds to variation in the reaction of sulfide with iron-phosphate compounds, while the production of ammonium in sediments is coupled to the activity of diazotrophs that are carbon- limited and, therefore, are regulated by primary productivity. Ammonium also would accumulate when sulfides block nitrification. These dependencies work as a positive feedback between primary production and nutrient supply and are predictive of the near-term effects of sea-level rise.