OS15D-01
The UK NERC Rapid Climate Change programme (RAPID) - a progress report
In order to determine whether changes in the North Atlantic thermohaline circulation (THC) are occurring due to global warming, in 2004 the RAPID programme (working with US scientists) deployed observational arrays across 26.5?N and along the western margin of the basin. These arrays will both monitor changes in the THC (strictly, in the MOC - meridional overturning circulation) and the propagation of signals in the deep western boundary current (DWBC). The DWBC is part of the lower limb of the THC and the means by which changes further north in the Atlantic propagate south. In addition, analysis of historical in situ observations is in progress to examine changes in the North Atlantic THC over the last 50 years. In conjunction with these observational studies, modelling and analysis of satellite data is being carried out to improve understanding of the processes and mechanisms by which the THC may be changing. This paper describes recent progress that has been made, presents some initial results from the observations, and describes plans for future work.
http://rapid.nerc.ac.uk/
OS15D-02
Detecting potential changes in the meridional overturning circulation at 26N in the Atlantic
We analyze the ability of an oceanic monitoring array to detect changes in the North Atlantic meridional overturning circulation (MOC). The observing array is 'deployed' into a numerical model (ECHAM5/ MPI-OM), and simulates the measurements of density and wind stress with approximate realistic observation density and errors. The simulated array mimics the continuous monitoring system deployed in the framework of the UK Rapid Climate Change program. We analyze a set of three realizations of a climate change scenario (IPCC A1B), in which - within the considered time-horizon of 200 years - the MOC weakens, but does not collapse. The simulated array is able to capture long-term changes in the MOC at 26N. For the detection analysis, we assume that the natural variability of the MOC is known from an independent source, the control run. Our detection approach accounts for the effects of observation errors, infrequent observations, autocorrelated internal variability and - to a limited extent - scenario uncertainty. With the number and type of observations simulated, and an assumed observation error of 1 Sv, a continuous observation of approximately 60 years yields detection with 95 percent reliability. Higher observation errors and lower observation frequencies result in lower detection frequencies. A simple cost-benefit analysis suggests that the economic value of information delivered by continuous MOC observations at 26N can far exceed the costs of the necessary observing system.
OS15D-03
Understanding and Attributing North Atlantic Freshening
Climate models predict an intensification of the hydrological cycle with possible implications for the thermohaline circulation of the ocean, as greenhouse gas concentration in the atmosphere increases. Recent reports from observational studies have shown a freshening trend in the sub-polar North Atlantic during the late 20th century. Is this part of that intensification already? If not, what is causing such a freshening trend? Using coupled climate model simulations, we try to understand and attribute the observed freshening. We show that a large part of the observed freshening may be linked to internal climate variability and freshwater redistribution, while the impact of global warming may have yet to be realised.
OS15D-04
Detecting Changes in the North Atlantic Meridional Overturning Circulation Using Oxygen Trends
Anthropogenic greenhouse gas emissions may trigger thresholds in the climate system leading to long lasting or irreversible climate change. Climate model projections of global warming suggest, for example, that the North Atlantic meridional overturning circulation (MOC) may persistently weaken or even collapse in response to anthropogenic climate forcing. The current climate change projections of the MOC response are, at this time, highly uncertain. An early detection of anthropogenic MOC changes would provide a warning sign that we are approaching one potential threshold in the climate system. However, detecting MOC changes is complicated by the high internal variability of the MOC signal, sizeable observation errors, as well as sparse and infrequent observations. Hydrographic tracers that are mechanistically linked to ocean circulation changes may provide essential information for early detection. Here we test whether the inclusion of oceanic oxygen measurements in an optimal fingerprint approach improves the detection MOC changes. To this end, we virtually deploy an MOC and oxygen observation array in the North Atlantic of a global ocean general circulation model. Our detection method accounts for key properties of the detection problem such as observation errors, infrequent observations, and autocorrelated variability. The oxygen trends show a higher signal-to-noise ratio than the MOC signal in the analyzed model. The optimal fingerprint combining the oxygen and MOC signals results in an earlier trend detection of MOC weakening than using just the MOC signal.
OS15D-05
Variability of Temperature in the Eastern China Seas in Recent 40 Years
Global warming is known as a remarkable phenomenon of the atmosphere-ocean system, which has been intensively studied. However, variability of temperature in marginal seas, especially in the China Seas, have been rarely studied and poorly understood. Based on historical data since 1950 combined with World Ocean Database 01 and other data sets from China, Korea, Japan, Russia and etc., interdecadal variability of temperature in the Bohai Sea (BS), the Yellow Sea (YS) and the East China Sea (ECS) in summer and winter is studied. Conclusions are drawn as follows. Trends of warming and cooling are both obvious in the study waters with complicated spatial patterns as shown by distribution of the changing rates of temperature, which are calculated by linear regression of temperature in $1\deg$x$1\deg$ squares with observations longer than 20 years. In summer, sea surface temperature (SST) showed warming tendency in the BS, the north YS, west part of the south YS and most part of the ECS including the Changjiang River Estuary (CRE), the Chinese coastal waters, and the Kuroshio and Taiwan Warm Current (TWC) regions, while cooling tendency in east part of the south YS and northeast corner of the ECS. With depth increasing, the warming regions shrank and cooling regions expanded in the YS, while the warming rates in the BS and the Kuroshio and TWC regions were intensified. Warming rates exceeding 0.05$\deg$C/a occupied the coastal zone of the western YS and ECS, and cooling rates exceeding -0.05$\deg$C/a near the Korean coast in the south YS. Warming rates in the Kuroshio region were about 0.01-0.02$\deg$C/a. In winter, temperature in the BS, most part of the YS and the northwest ECS including the CRE adjacent areas cooled down, while that in coastal part of the ECS (the TWC region) and regions of the Kuroshio and the Yellow Sea Warm Current (YSWC) origin warmed up. Spatial patterns of warming and cooling were similar at different depths. Cooling rates were larger than -0.05$\deg$C/a in the central BS, the central south YS and near the CRE, and warming rates exceeded 0.05$\deg$C/a near the Chinese coast in the ECS and 0.02$\deg$C/a in the Kuroshio-YSWC region, respectively. The trends in summer and winter indicated that amplitudes of seasonal cycles in the BS, the western YS and the CRE adjacent waters tended to become larger from 1950's to 1990's. Interdecadal variability of temperature is further studied in 5 regions chosen in the BS, the north YS, the eastern part of the south YS, the CRE adjacent waters and the Chinese coastal waters in the ECS, where data densities are relatively higher. Interdecadal fluctuations of temperature with amplitudes of 5-10$\deg$C were found in the BS in summer, with troughs in 1970 and 1985, and summits in 1973 and 1990. Despite scarcity of data, it was clearly indicated that mean temperature in the BS in winter in the 1980s was generally lower than that in the 1960s by about 2$\deg$C. Temperature variability of the other four regions was dominated by interannual fluctuations in both summer and winter, and the long term trends were in accordance with discussed above.
OS15D-06
Influences of climate change on Great Lakes ecosystem: A review of possible impacts of long-term changes.
Global warming is under way and already causing changes to our environment. Much uncertainty remains about specific ecological and economic changes that a warmer climate with drier summers will bring to the Great Lakes region, but it is certain that the impacts will magnify in importance in the future. This knowledge provides no excuse for inaction or fatalism, however,because innovative, affordable, and prudent solutions are available to help reduce the severity of climate change globally, increase the health and resilience of ecological and economic systems vital to the region, and begin planning and preparing now to adapt to those future changes that cannot be avoided. The Great Lakes is home to 60 million people whose actions can profoundly affect the region's ecological bounty and the life-sustaining benefits it provides. Now that the world is entering a period of unusually rapid climate change, driven largely by human activities that release heat-trapping greenhouse gases into the atmosphere, the responsibility for safeguarding our natural heritage is becoming urgent.
OS15D-07
ECOSYSTEM RESPONSES TO RECENT WARMING IN THE SOUTHEASTERN BERING SEA
During the past decade, the southeastern Bering Sea has experienced an overall trend of diminishing seasonal sea ice cover, increasing water temperatures and increased stratification. Ecosystem responses have included changes in the timing of the spring bloom, summer blooms of species heretofore rare in the southeastern Bering, decreases in summer zooplankton biomass, including that of jellyfish, and shifts in species composition, northward shifts in the distribution of some fish species, and continuing declines in northern fur seal populations at the Pribilof Islands. Population declines of seabirds at the Pribilofs may have stabilized or reversed for some species. Ecosystem responses reflect changes in the pathways of energy through the ecosystem. Although the interannual signal is strongest for the physical parameters, many of the responses of upper trophic level species occur over longer time-scales. The strong interannual variations in the physics provide the opportunity to identify mechanisms that will be important in determining how future climate change may affect the marine ecosystem of the eastern Bering Sea.
OS15D-08
High Precision Monitoring Of Coastal Erosion in The Inupiat Eskimo Village Of Barrow Alaska
Coastal erosion is one of the many impacts resulting from global climate change in the Arctic. Sea ice in the Arctic ocean is decreasing in extent and is also becoming less thick allowing wave height to increase, which in many areas can enhance coastal erosion. In northern Alaska, the rate of coastal erosion appears to have increased dramatically over the last 50 years. Along the 2 kilometers of coastline used in this study, approximately 236000m^2 of coastal tundra has been lost to coastal erosion since 1948. This is cause for concern because of the increased potential damage to property, archeological sites and the ecology of the Arctic system. The central objective of this study was to determine the extent and nature of coastal erosion since the last survey conducted in 2003. Surveys were conducted on foot using a Differential Global Positioning System (DGPS) and compared to previous surveys using a Geographic Information System (GIS). In particular, this survey was compared to those conducted by Dr. Jerry Brown in 2003. This project will serve as a continuation of coastal erosion surveys and will be added as legacy data to the Barrow Area Information Database-Internet Map Server (www.baidims.org).
http://baidims.org
OS15D-09
The Effect ENSO has on the Economies of Countries in the Tropical Pacific
The effect El Niño Southern Oscillation (ENSO) has on the economies of those countries whose climate is most directly influenced by the phenomenon (those countries that border the Tropical Pacific) is studied. World Bank economic indicators are compared to the ENSO signal, as revealed by sea surface temperatures. The analysis suggests that the changes in climate brought on by the onset of El Niño affect those parts of the economy directly affected by the weather (agriculture, energy production, tourism, transportation). The economic impact spreads to other related industries eventually affecting most sectors of the economy as well as national economic indicators such, as Gross Domestic Product (GDP). Countries where agriculture comprises a smaller segment of the economy are as affected by ENSO as those countries that are more reliant on agriculture. It is proposed that the changes in climate have an impact on regional food availability so that countries dependent on food imports must compensate. Also, those countries dependent on water sensitive crops appear to be most sensitive to changes in climate. Political considerations can also affect the connection between the climate and economy.
OS15D-10
Reversible Inhibitory Effects of CO2 on Marine Phytoplankton
It is shown here that carbon dioxide gas has dramatic inhibitory effects on photosynthesis and pigmentation in representative species from six divisions of cultured marine phytoplankton and two natural sampling sites in Monterey Bay. Oxygenic photosynthesis, measured over short 5 min intervals, was inhibited as a function of increasing CO2 concentration added to seawater media. At the highest CO2 levels tested, photosynthesis was zero. The cellular content of ATP also decreased after treatment with CO2. Photosystem II variable-fluorescence parameters were altered under high-concentrations of CO2; specifically, photochemical quantum efficiency (Fv/Fm) decreased and non-photochemical quench (NPQ) increased. Parallel changes in the ratio of xanthophyll cycling pigments, diatoxanthin/diadinoxanthin, accompanied the trends in variable fluorescence parameters for those species containing xanthophyll-cycling pigments. All parameters described above reacted on similar rapid time scales (<5 min). The effect of CO2 on photosynthesis, Fv/Fm and NPQ was reversible by returning the media to air saturation. Collectively, the sequence of physiological responses above mimics all the well-documented traits typically associated with photoprotection, including repetitive reversibility. However, in this case, the `photoprotective' response sequence was triggered by CO2 under extremely low irradiance levels (< 5 uEin m-2 s-1), below the compensation intensity for photosynthesis. Comparative experiments using similar acid-induced pH reductions from CO2 and other inorganic acids suggest the effects above are due to CO2 and not to pH changes per se.
OS15D-11
Marine Zooplankton and Microbial Survival Under Elevated Carbon Dioxide: An Experiment
A growing body of research has shown that elevated concentrations of dissolved CO$_{2}$ can be deleterious to marine organisms. This has relevance in anticipating the impacts of the ongoing increase in ocean CO$_{2}$ (via anthropogenic CO$_{2}$ air-sea invasion), as well as in predicting the consequences of proposed, purposeful injection of CO$_{2}$ into the ocean as a CO$_{2}$ sequestration option. On the other hand, local introduction of CO$_{2}$ could provide an inexpensive and easily-dissipated biocide for invasive and nuisance aquatic species control, in particular for ballast water and biofouling treatments. To quantify CO$_{2}$ effects on plankton survivorship we incubated darkened 200L containers of seawater containing resident zooplankton and microbes from San Francisco Bay, and aerated with ambient, 1%, or 10% CO$_{2}$ gas/air feeds. Over 5 days we observed a near 100% reduction (relative to controls) of live zooplankton in the 10% CO$_{2}$ treatments. This sensitivity to CO$_{2}$ is significantly higher than anticipated from pH effects alone. Also, O$_{2}$ concentrations were greater than 8 mg/L in all treatments, and thus not a factor in the mortality observed. Viable zooplankton numbers remained at very low levels for 7 days after the CO$_{2}$ treatments were ended, implying a significant, long-term impact to the initial resident community. The 1% CO$_{2}$ treatments removed up to 30% of zooplankton, with some species specificity evident in this removal. This mortality rate was also higher than expected from pH effects, although significant community regrowth was found 7 days after termination of the gas treatment. In contrast to the zooplankton results and contrary to expectations, significant reductions in algal and microbial abundance and activity ([POC], [PON], C/N, [ATP], [chlorophyll]) relative to controls was not evident in any of the CO$_{2}$ treatments. The preceding observations will be discussed in the context of both passive and intentional CO$_{2}$ introductions to seawater.
OS15D-12
Free Ocean Carbon Dioxide Enrichment (FOCE): Control and Measurement of Ocean Seawater to Simulate a Low pH-High CO$_{2}$ Ocean
Scientists and Engineers at the Monterey Bay Aquarium Research Institute (MBARI) have undertaken a series of small-scale in-situ CO$_{2}$ enrichment experiments in order to simulate the present and predicted future effects of fossil fuel CO$_{2}$ emissions on ocean pH. In excess of 25 gigatons CO$_{2}$ are released to the atmosphere per year and the ocean has been the primary sink of these emissions. Presently, the ocean is absorbing on average 1 million tons of fossil fuel CO$_{2}$ per hour. The result of this process has been a lowering of the surface ocean pH by approximately 0.1 units during the past 100 years. Recent geochemical models project an additional drop of 0.2 units by the middle of this century. The FOCE prototype was designed to create a controlled lowered pH condition for a freely exchanging volume of seawater 0.5 meters high by 1.0 meters diameter. A current meter and pH probes in the center of this volume provide the control feedback for driving the system to a desired pH set point (0.1 to 0.3 pH units below ambient seawater pH). The prototype system used a rotating mechanical vane and valve with 8 ports, each port delivering acidified seawater to emitters that covered 1/8$^{th}$ the circumference of the 2 meter diameter framework. The directional valve delivered acidified seawater primarily to the upstream side of the FOCE structure. A second-generation FOCE system will use a current meter, directional resolver and electronic operation of up to 16 solenoid valves, allowing for significantly improved directional control at low flow conditions (< 10 cm/sec). For the two sea trials conducted thus far with the FOCE prototype system, HCl was used to lower the pH of the seawater. We have now begun to envision a FOCE design that would use liquid CO$_{2}$ to change the local pH chemistry. A near shore cabled observatory could provide the power, communications, and a supply of piped CO$_{2}$ necessary for long term (weeks-months) observation and control of depressed pH levels in an ocean environment.
http://www.mbari.org
OS15D-13
A Decade of Biogeochemical Investigations at the European Time Series Station ESTOC
Basin wide modeling studies have revealed a clear asymmetry of the biogeochemistry across the subtropical North Atlantic gyre, mainly relating to the magnitude and processes of nutrient supply and new and export production. Time-series measurements of the actual biogeography are needed to confirm and understand the inherent variability. Here we present time-series measurements carried out in the eastern boundary system of the subtropical North Atlantic gyre at the European Station for Time-Series in the Ocean, Canary Islands (ESTOC), located 100 km north of the Canary Islands. Standard water column properties have been measured at the station since 1994 in monthly intervals; monthly measurements of pCO2 were added in 1996. Primary production has been inferred from the in situ chlorophyll concentration by applying a bio-optical model and by satellite and amounts to about 12 mol C m-2 yr-1. Particle flux has been measured with moored particle traps at the station since 1991, supplemented by surface tethered traps in some years. Particulate organic carbon export extrapolated to 150 m depth amounts to about 0.2 mol C m-2 yr-1, determined both by surface-tethered and shallow moored sediment traps. Net CO2 fluxes at ESTOC are positive with an average value of 0.05 mol CO2 m-2 yr -1, mainly controlled by SST and by the predominant Trade Winds. Net community production determined by the biologically induced drawdown of dissolved inorganic carbon amounts to 2-4 mol C m-2 yr-1 when integrated over the mixed layer. Nitrate input into the mixed layer by wintertime convection allows a potential new production of about 0.2-1 mol C m-2 yr-1 depending on the depth of wintertime convection. In addition to showing the seasonal and interannual variability in its biogeochemistry, we will intend to reconcile the physical and biological components of the carbon balance and nutrient budgets at ESTOC.