OS11D-1145
Suspended sediment flux in a muddy mesotidal estuary: tidal and meteorological forcing, and sensitivity to climate change
Data from a 1 year acoustic Doppler profiler deployment in a muddy mesotidal estuary on the UK east coast are analysed to reveal the sensitivity of the suspended sediment dynamics to tidal and meteorological forcing. Flux calculations indicate a small sediment import equivalent to just 1.5% of the gross flood tide transport. Although little confidence can be assigned to either the magnitude or direction of such a small residual when considered in isolation, the inference that the sediment regime is finely balanced is qualitatively supported by the close similarity between flood-tide and ebb-tide SSC values. Singular spectrum analysis of the SSC time series reveals expectedly large contributions to the variance in SSC at intratidal and subtidal (semimonthly and monthly) scales but also picks out intermittent variability that is initially attributed to a combination of nontidal surge and wind stress forcing. Closer examination of the data through cross- correlograms and event-scale analysis implicates meteorological forcing as the major factor. Acting through the resuspension of intertidal mudflat sediments at times of strong westerlies, meteorological forcing is directly implicated in episodic sediment export from the estuary. Thresholding of tide-averaged fluxes using a range of critical wind stress values further indicates that 'tide-dominated' (i.e. low wind stress) and 'wave- dominated' (high wind stress) conditions are associated with sediment import and export. Sediment balance is potentially sensitive to the frequency of high wind stress events, since the associated sediment exports are several times larger than the average import under calm conditions. Intermittent meteorological forcing may thus exert an important control on the sedimentary balance of what are generally thought of as tidally- dominated muddy estuarine systems. These findings may have wider implications for a broader set of estuaries within the southern North Sea and, more generally, suggests that the role of wind climate should not be overlooked in studies of estuary response to environmental change.
OS11D-1146
The Meteorological Influences On The Long-term Variation In Nutrient Concentration In The Seto Inland Sea, Japan
Global climate change begins to impact on coastal environment, as represented by sea-temperature rises. In the Seto Inland Sea, Japan, a semi-enclosed sea facing the Pacific Ocean, bottom temperatures rise at the rate of ~ 0.03 deg.C per year (Takahashi and Shimizu, 2004). In this study, the results from observation and numerical simulation for a 30-year period are analyzed in order to elucidate the influences of long-term variations in meteorological forcing on biogeochemical processes in a coastal sea. Significant relationships between the amount of solar radiation and bottom temperature, bottom concentrations of dissolved oxygen and dissolved inorganic nitrogen (DIN) have been found, suggesting solar radiation largely controls the stratification and thus the amount of nutrients stored on the bottom of the semi-enclosed sea. The relative importance of each meteorological parameter and long-term rises of temperature on the variations in nutrient concentration will be shown in the presentation.
OS11D-1147
Comparison of the sea cover properties in eastern Canadian Beaufort Sea as observed with helicopter-borne sensors in April 2004 and April 2008.
During April 2004 and April 2008, ice property data were collected by helicopter-borne sensors and satellite- tracked ice beacons. Ice property data was collected along helicopter flight paths over the land-fast ice and over the mobile pack ice in the eastern Canadian Beaufort Sea (Amunsden Gulf) using an Canadian Ice breaker over-wintering in the Arctic pack ice as a logistic base. Ice thickness, surface roughness data were collected with an Electromagnetic-Laser system and lead/floe distributions with a Video-Laser system. The data is used to validate algorithms to identify ice properties seen as ice signatures in SAR satellite imagery. September Arctic sea ice extent shows that 2004 and 2007 were respectively the start and the continuation of the rapid decline of ice extent within the Arctic. The April sea ice properties reflect this change in the Amunsden Gulf. The land-fast ice extent and thickness were less, mobile ice were thinner and the thin ice extent (0-20cm thick ice) rarely present in 2004 were extensively found in 2008 with areas of up to 50km in width. The 2008 pack ice (lower ice extent) was more mobile under the wind forcing. An thin (60cm thick) flaw lead 20km wide and 200km long was ridged into a 2km wide 10m rubble field and then open up again to 20km providing additional salt rejection to the ocean by renewed thin ice growth even though the air temperatures were below normal. So does the lower ice extent and more mobile first year ice conditions lead to a tempo rarely increase in first year ice ridging and ice volume (and salt rejection to the ocean).
OS11D-1148 [WITHDRAWN]
North Pacific Gyre Oscillation Controls Phytoplankton Dynamics in Hong Kong Coastal Waters
The coastal waters of Hong Kong have been influenced by a number of anthropogenic factors, including cultural eutrophication, land reclamation and dredging. The effects of climatic variability on phytoplankton dynamics may be difficult to discern in coastal ecosystems due to the interaction of climatic variability with anthropogenic effects. In this study, the influence of the El Nino-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO) on phytoplankton dynamics in Hong Kong coastal waters was examined from 1986-2004. Weak correlations were found to exist between chlorophyll a concentration (Chl) and the multivariate ENSO index and PDO index. However, strong correlations were found to exist between the NPGO index and Chl. The NPGO has been proposed to influence Chl concentration in the North Pacific through its influence on upwelling and nutrient concentrations. In the coastal waters of Hong Kong, which are highly impacted by cultural eutrophication, we propose a different mechanism. The NPGO is locally forced by surface wind variability and we have found a strong negative correlation between NPGO and wind speed in Hong Kong. By destabilizing the water column, high wind speeds are detrimental to phytoplankton growth and therefore we hypothesize that the relationship between the NPGO and phytoplankton dynamics is as a result of wind speed variability. We have shown that large scale modes of climatic variability can be important in controlling phytoplankton dynamics even in ecosystems which are markedly influenced by a number of anthropogenic factors.
OS11D-1149
Benthic Foraminifera and Testate Amoebae (Thecamoebians) as Hydrologic Proxies of Subterranean Water Masses: Evidence from Aktun Ha (Carwash) Cave System, Mexico
For the first time, foraminifera and testate amoebae have been systematically examined in a coastal phreatic cave system—a 'subterranean estuary'. Abundant communities of modern testate amoebae and relict foraminifera were recovered from the anchialine cave Aktun Ha (Carwash) Mexico. During the Sangamon Interglacial (MIS 5e) highstand, saline water flooded the cave passages to host a Marine Assemblage of the foraminifera Bolivina sp. (mean 73 percent) and Elphidium sp. (mean 11 percent) with a mean δ13C = -5.5‰ and δ18O = -2.7‰. In vadose cave conditions of the Pleistocene lowstands, travertine precipitated over sediments containing the Marine Assemblage. Holocene sea level rise re-flooded the cave with freshwater, allowing for colonization of a Freshwater Assemblage dominated by testate amoebae Centropyxis aculeata (mean 38 percent) and Arcella vulgaris (mean 10 percent) with a mean δ13C = -10.8‰ and δ18O = -4.9‰ measured on Cytheridella ilosvayi ostracods. These results demonstrate that subterranean void spaces are a suitable environment for colonization by shelled protists. Since climatic and sea level shifts alter hydrologic and geochemical composition of coastal groundwater masses, these results provide promise that shelled protists can be longer-term proxies for monitoring hydrologic and geochemical variables in subterranean coastal water systems.
OS11D-1150
Sediment accumulation in the Siletz River estuary in response to changes in hydroclimate and land use.
The transfer of sediment from source to sink involves a complex set of processes that vary over multiple time and space scales. In the Pacific Northwest, there is anecdotal evidence that many estuaries are filling rapidly with sediment due to changes in hydroclimatology coupled with land-use changes. Because both factors may co-exist, the relative contribution of each, the mechanisms of sediment delivery (event vs. steady), and the role of larger scale processes, such as sea level rise, are important issues to disentangle. To address these issues we are studying the Siletz River, a small (<1000 km2), mountainous river system in the Oregon Coast Range. Precipitation and stream flow patterns in this region are forced by the PDO-ENSO, with a cool, wet period from 1945 to 1975. In addition, the Siletz watershed was extensively logged following WWII, thereby exacerbating sediment erosion from the watershed. A variety of evidence (e.g., x-radiographs, grain size, C-14, Pb-210 and Cs-137 geochronology) collected within the estuary indicates, however, that there has not been a clear acceleration of sediment accumulation during the latter half of the 20-th century, and suggests extrabasinal effects (e.g., sea level rise, neotectonics) may control accumulation.
OS11D-1151
The role of extra-tropical to tropical Pacific Ocean exchanges in the variability of ENSO in CCSM3
In this manuscript we have attempted to investigate mechanisms that force the interdecadal variability of ENSO magnitude and frequency in an effort to help explain the apparent shift in ENSO behaviour seen during the late 1970's. We have chosen to focus particularly on the extra-tropical Rossby wave mechanism. Results from oceanic shallow water models show that the Rossby wave theory is a valid mechanism for altering the equatorial thermocline depth and for modulating the amplitude of modelled ENSO events. However, questions remain over whether the mechanism operates in more complicated CGCMs (especially z- coordinate types) and if so, whether it generates a large enough equatorial or ENSO modulating response to be seen above the noise level of the equatorial Pacific Ocean. We firstly set out to confirm that the Rossby- Kelvin wave mechanism operates in more complicated (z-coordinate) CGCM models. We then used a model surgery approach called Partial Coupling (PC) to help isolate the role of wind stress forced oceanic exchanges between the extra-tropics and the tropics on modelled ENSO variability. We find that changes in the background state of the equatorial Pacific thermocline depth induced by a fixed off-equatorial wind stress anomaly forcing have a significant effect on the amplitude of the modelled ENSO events. Therefore, confirming the results from simpler models and further validating theories that rely on oceanic wave dynamics to generate Pacific Ocean decadal variability. As such, we believe that a comprehensive understanding of seasonal-to-interannual prediction of ENSO variability can be gained by a better understanding of extra- tropical to tropical Pacific Ocean transfers and western boundary processes. Further, we believe that these results may provide a physical basis to enhance multiyear probabilistic predictions of ENSO indices.
OS11D-1152
Multi-proxy records of estuarine ecosystem response to Late Holocene climate variability, Chesapeake Bay, USA
Late Holocene climate variability, including the Medieval Warm Period (600-1100 AD) and Little Ice Age (1200-1900 AD), influenced temperature, precipitation, and atmospheric-oceanic interactions on decadal to centennial time scales throughout the North Atlantic region. Complex interactions among climate patterns such as the North Atlantic Oscillation, El Niño Southern Oscillation, and Atlantic Multidecadal Oscillation serve to amplify or dampen climate variability, and the superposition of anthropogenic atmospheric greenhouse forcing and land-cover changes further complicate predictions of climate trends. We present results from analyses of pollen, ostracodes, benthic foraminifers, diatoms, bulk-sediment stable isotopes, compound-specific isotopes, trace elements from shells, and biomarkers from Chesapeake Bay sediment cores and use them to evaluate late Holocene trends in temperature, precipitation, salinity, and productivity. These multi-proxy records provide robust documentation of past climate variability and ecosystem responses during an interval that includes the warm, dry Medieval Warm Period and the cool, wet Little Ice Age. These climate-driven ecosystem fluctuations prior to anthropogenic changes in the Chesapeake Bay watershed had significant impacts on estuarine stratification, seasonal hypoxia, productivity, biodiversity, and distribution of coastal vegetation. These long-term datasets provide a critical perspective to evaluate recent changes, establish restoration targets, and predict likely responses of estuarine ecosystems to land-use and climate change scenarios.
OS11D-1153
Ocean Processes Driving the Phenology and Productivity of Marine Birds in the California Current System
We will examine the effects of local ocean conditions and basin-scale patterns of climate variability on phenology and productivity of five species of marine birds to assess how long-term changes in ocean conditions are affecting marine bird populations and to provide insight into how populations may respond to predicted changes in the marine environment under various climate change scenarios. We will focus on Cassin's Auklets, Common Murres, Pigeon Guillemots, Brandt's Cormorants, and Pelagic Cormorants. We will conduct the analyses using an Akaike's Information Criterion approach to model selection, with spring transition date, upwelling strength, and sea surface temperature as measures of local ocean conditions and the Southern Oscillation Index, the Pacific Decadal Oscillation, and the North Pacific Gyre Oscillation as basin-scale measures of climate variability. We will evaluate the relative importance of local versus basin- scale processes on observed trends in seabird breeding phenology and productivity from 1972-2007.
OS11D-1154
Impact of Hurricane Isabel on Hypoxia in Chesapeake Bay
Episodic forcing by tropical storms and hurricanes often consists of high winds, heavy precipitation, increased freshwater flow, strong vertical mixing, and intense pulses of nutrients, leading to enhanced plankton biomass and temporary relief or termination of hypoxic condition in estuaries and coastal oceans. The U.S. East and Gulf Coasts have experienced elevated tropical storm and hurricane activity in recent years, a pattern expected to persist for several more decades and that may increase due to global warming. Therefore, there is an urgent need to understand the mechanisms governing the response of a coastal ecosystem to extreme weather events. Here we present a preliminary modeling investigation into Chesapeake Bay's response to Hurricane Isabel which made landfall at the Outer Banks of North Carolina and moved past the Bay on 18 and 19 Sept 2003. Strong storm winds eroded stratification and produced strong turbulent mixing which injected bottom nutrients to the surface euphotic layer and aerated the hypoxic bottom water. After the passage of the storm, however, the horizontal salinity gradient drove restratification and return to hypoxia in bottom water as well as producing a post-storm phytoplankton bloom. Using a coupled hydrodynamic-biogeochemical model, we conduct numerical experiments to investigate how the hurricane-induced destratification and restratification cycle affects the distribution of dissolved oxygen in Chesapeake Bay and explore the mechanisms responsible for the observed rapid return of hypoxia after the storm.
OS11D-1155
Flood-Induced Surface Blooms Alter Deep Chlorophyll Maxima Community Structure in Lake Michigan.
Watershed-wide floods can bring increased nutrients and phytoplankton to receiving waters. This input can alter physical, chemical and phytoplankton community structure in a major way. Phytoplankton species composition and size distribution are key factors in their use as ecological indicators. Since 2003, phytoplankton communities in Lake Michigan have shifted from diatom and big cell (>10μm)- dominated to small cell picocyanobacteria-dominated phytoplankton (<3μm). Picoplankton typically thrive under lower light conditions than diatoms, are adapted with phycobiliprotein pigments for deepwater light quality, have a higher surface-to-volume ratio for effective nutrient scavenging, and are smaller than the preferred range (5-100μm) for filter-feeding mussel populations. After only five years with Quagga Mussels, dampened seasonal cycling of silicate indicated a basin-wide reduction of diatom production, and unicellular Cyanobacteria became dominant in deep chlorophyll maximum (DCM) zones. In the DCM, Synechococcus-like cells reached populations of at least 210,000 cells/ml. DCM chlorophyll (chl) remained similar (3-4μg/l) but late summer species composition changed dramatically to mostly <3μm cells. During the June 2008 Midwest floods, the rivers into Lake Michigan discharged at over 30 times the rate of water typically flowing into the lake. Nearshore phytoplankton were dominated by diatoms localized in the epilimnion (upper 5-10m). Chl increased several-fold in surface waters and diatom biomass increased from the previous years. The 1% PAR penetration changed from 35-40m previously to only 25m in 2008. Chl in the >10μm fraction increased from previous years, and over 75% of the particulate Si was also in this size fraction. Because of the rapid sinking of diatoms during calm weather of late June-early July of 2008, particulate Si did not reach high values in surfaces waters (ca. 1.5μM) but remained at a consistently higher level than in 2007. Sinking of diatoms from the surface depleted chl in a progression from inshore to offshore during July 2008. In July surface chl was higher 40-70 km offshore than in the coastal zone. Surface phytoplankton waxed and waned in population density as if a wave or lens moved continuously further offshore, with sinking cells depleting the surface algae following behind the crest. In the wake, strong DCM populations with higher chl and particulate Si accumulated in the 30-45m zone at the bottom of the thermocline. However, in 2008 DCM zones, picocyanobacteria attained only 70,000 cells/mL, one-third of the same dates in 2007. The ratio of chlorophyll per Synechococcus cell in 2008 was about 5-fold higher than in 2007, corroborating microscopic observations of lowered picoplanktonic abundance and proportion of total phytoplankton biomass. It appears that decreased PAR penetration and competition with sinking diatom populations prevented picoplankton from attaining the high populations and ecological dominance they enjoyed since the quagga mussel invasion. The episodic nature of this change will be proved if the previous conditions are again observed in 2009.
OS11D-1156
Hindcast simulation with a hydrodynamic sea shelf model from 1948 till 2007 -- a model study.
A challenging question is whether there is a systematic climate change in the North Sea and which physical processes play an important role. To study this numerical model runs are done for the period of 1948 till 2007. For the simulations the 3-dimensional barocline shelf sea model HAMSOM with a spatial resolution of 20' x 12' and 19 levels is applied. The simulation is forced with the NCEP/NCAR Reanalysis 1 data set which included air temperature, humidity, cloud cover, precipitation, sea level pressure and wind components. The boundary conditions for the open seas are from a climatological data set (Levitus, 1982) and also eight partial tides are included. Model results show good agreement with long time measurements. Results and trends for temperature and heat content will be discussed.
OS11D-1157
Wind-Induced Redistributions of Hypoxic Water in Chesapeake Bay
Anthropogenic nutrient enrichment has contributed to the depletion of oxygen from bottom waters in Chesapeake Bay. Despite the major public commitments to reduce nutrient loading, the Bay continues to experience hypoxia and deteriorating water quality. A major impediment to developing successful restoration strategy is the complicating effect of climate variability and weather events. In particular, episodic wind events exert subtle and not-well-understood controls on key biogeochemical processes. Here we present a modeling investigation into the effects of summer winds on the distribution of dissolved oxygen in Chesapeake Bay. Southerly winds drive deep hypoxic water up into shallow areas toward the western shore, producing episodic hypoxia in shoal regions that are normally well-oxygenated. In contrast, northerly winds drive deep hypoxic water toward the eastern shore. At the same magnitude southerly (upestuary) winds tend to produce stronger mixing, weaker stratification than northerly (downestuary) winds due to the wind straining effect, with implications for hypoxia. Although the prevailing direction of summer winds is southerly, isolated strong northerly winds lead to substantial reductions of hypoxia. To quantify the wind effects on hypoxia, we calculate net oxygen transport across the pycnocline and horizontal fluxes through the bottom layer.
OS11D-1158
Midwest Flood of 2008: Lake Michigan Basin-Wide Summer Plankton Bloom is not due to Nutrient Injection
Major Midwestern US flooding occurred in June of 2008 following over 30cm of rainfall in a 4-day period. Tributaries to Lake Michigan swelled, with outflow from the Milwaukee River increasing 30-fold from long-term means of 8.5 m3/s to over 250 m3/s. Flood stage was sustained for 8 days and dampened over a protracted 30-day period. A series of inshore, transect, and mid-lake cruises established the presence of unseasonally strong gradients in surface phytoplankton biomass moving progressively offshore, to ultimately influence at least half of the 150 km-wide Lake Michigan basin. Remote sensing of chlorophyll (chl) and the diffuse attenuation coefficient (at 490nm) documented the existence of blooms offshore of each major river on both sides of the lake persisting into mid-July, and then disappearing from surface waters, not visible to space-based satellite sensors. Profiles detailed deep chlorophyll maxima that were distinct from previous years. Surface transects in 2007 yielded typical summer chl of <0.5μg/L, with little deviation over the mid-lake seamounts. In July 2008, surface chl over deep water reached concentrations as high as 1.7μg/L, with distinct depletions (25%) over the quagga mussel-infested shallower reef zone. Offshore transects displayed high chl in the upper 5m only a few days after the onset of high flow. Unseasonably high phytoplankton population densities progressed with time and distance offshore in a manner suggestive of advection of a surface lens across the well-stratified lake. As the lens progressed offshore, populations continued to grow, appearing as a band of high chl extending across the lake. After 2 weeks, inshore areas had substantially lower surface biomass than those offshore, reflecting settling of denser cells during a long period of relatively calm weather. Development of deep chlorophyll maxima (DCM) at 25-40m followed the decrease of surface populations at all locations deeper than 50m. High satellite- derived diffuse attenuation coefficients also reflected the presence of dense algal populations in the upper water column. 1% PAR penetration reached to only 25m, substantially short of the 35-40m characteristic of the previous 5 years. In some cases, extinction coefficients were higher in the upper 5m than in deeper water, again consistent with biomass observations. Compared to 2007, biomass as chl and particulate Si were exceptionally high for stratified waters. It would be expected that flood-stimulated plankton blooms resulted from nutrient enrichment from outflows but this was not the case for macronutrients (N, P, Si). Available P is typically <40nM all year in offshore Lake Michigan, and 2008 was no exception. Slightly enriched harbor outflow water decreased to <40nM within 3-5km from shore during the peak of runoff. Si was >100μM in the harbor, but is over 20μM in open lake waters and hence not limiting diatom growth; even so, the harbor signal was muted within a few km of shore. Nitrate is consistently 25-30μM in the open lake, and outflow source waters were barely twice that level. There was no chemical evidence of source water at repeatedly sampled stations 20-70 km offshore, though plankton populations were conspicuously enriched. Although iron could be a factor (not measured), we favor turbulence and inoculation of typically oligotrophic offshore waters with seed populations encountering initially clear water with little competition for the photosynthetic niche, and no predation by the underlying quagga mussel beds.
OS11D-1159
Vertical Structure Variability of the Mesoscale Activity off Western South America During El Niño 1997-98: Connection With the Equatorial Kelvin Wave
Oceanic variability along the western coast of South America is influenced by the equatorial Kelvin waves (EKW) at a variety of timescales, from intraseasonal to interannual frequencies. Coastal-trapped waves (CTW) originating from the equator can propagate along the coast, modify the stability of the regional current system and trigger extratropical Rossby waves (ERW) north of the critical latitude as well as eddies. In this study, an eddy-resolving regional circulation model forced with observed winds and realistic boundary conditions over 1992-2000 is used to investigate the impact of the EKW on mesoscale activity in the eastern South Pacific, with a focus on the strong 1997-98 El Niño event. The simulation reproduces realistically most aspects of the observed variability, namely sea level variations at the equator and along the Peru-Chile coast, structure of the coastal current system, and spatial/temporal variations of mesoscale eddies near the coast and in the inner basin. Space-time spectral analysis of sea level and subsurface currents at the equator and along the coast allow characterizing wave propagations and identifying the associated dominant frequencies. A vertical mode decomposition of the model variability is then used to document the propagation of the CTW and ERW. The first baroclinic mode ERW is shown to ventilate most of the region, whereas higher-order modes are confined close to the coast, having energy in the forms of both CTW and ERW. The modal decomposition also allows documenting the vertical structure variability of eddies through the estimation of the baroclinic mode contribution to the EKE for the most energetic modes. Gravest mode eddies are shown to have similar propagating characteristics to the ERW whereas higher-order mode eddies remain in the near-shore region. In the light of these results, the link between mesoscale activity and the equatorial Kelvin wave is investigated focusing on the intraseasonal frequency band (50 to 120 days). It is shown that prior to the development of the 1997-98 El Niño, the intraseasonal equatorial Kelvin wave exerted a significant control on the regional circulation.
OS11D-1160
Seasonal Patterns of Flood, Wind, and Wave Coherence Along the US West Coast: Implications for Sediment Dispersal and Deposition.
Small rivers with mountainous catchments account for over half of the terrigenous material delivered to the coastal ocean. Dispersal, deposition, and cycling of sediments and associated nutrients ultimately influence shelf carbon budgets. Recent work on collision margins revealed that these small rivers flood during energetic ocean conditions, creating conditions conducive to dispersal of sediments via multiple sediment transport mechanisms. Furthermore, the relative timing of the peak flood and peak wave conditions influences dispersal and depositional patterns. Our study sought to identify patterns of fluvial and oceanic coherence along the US west coast by analyzing 10 years (1996-2006) of NOAA buoy, Climate Prediction Center storm track, and USGS gauge data. Discharge, buoy data, and storm tracks for the Umpqua, Eel, Salinas, and Santa Clara rivers and their adjacent shelves revealed temporal and spatial coherence patterns of wave event and flood magnitude, frequency, and timing. The seasonal period of energetic waves for each river-shelf system began 1-2 months earlier than the flood season (November) and extended 1 month beyond the end of flood season (May). There was also a seasonal disconnect in the timing of peak wave energy (December) and peak floods (January to February). Peak flood activity occurred in January on the Umpqua and Eel Rivers, and in February for the Salinas and Santa Clara Rivers. Flooding and wave events were more frequent and greater in magnitude on the Eel and Umpqua river shelves. The Salinas and Santa Clara rivers displayed lower fluvial inputs, but Salinas River shelf wave events were greater in magnitude. The magnitude and timing of peak waves and peak discharges during floods varied characteristically for each river-shelf system. Peak discharge and peak wave magnitude during floods generally decreased from December to May, indicating that dispersal and depositional patterns vary over the season. Additionally, the timing between peak river discharges and peak waves during floods revealed that waves tend to be most energetic before the peak discharge on the Eel and Umpqua Rivers. Peak waves generally occurred after the peak discharge on the Salinas and Santa Clara Rivers. The timing of waves and floods for each river-shelf system was correlated with storm movement and characteristic wind patterns. For example, from January through May, storm tracks shifted northward of the Eel River shelf, resulting in a wind shift from south to north winds, and an increasing disconnect between peak wave energy and peak discharge.
OS11D-1161
Climate Variability and Change in a Eutrophic Great Lakes Freshwater Embayment: Shifting Hydrodynamics and the Potential for Indirect Impacts on Biogeochemical Processes, Carbon Cycling and Hypoxia
Future changes in the climatic regime of the Great Lakes region have the potential to induce a variety of both direct (e.g. thermal) and indirect (e.g. biogeochemical) alterations in ecosystem function. In the case of the later, we have identified a statistically significant shift in wind direction of the average wind field over the Great Lakes basin that is consistent with a southward migration of the dominant summer storm track. In Green Bay (NW Lake Michigan), we have shown that the new wind field has most likely resulted in periods of decreased thermal stratification and an overall decrease in water mass exchange with Lake Michigan. In subsequent studies, aimed at determining the impact of these shifts in the physical climate regime, time series measurements of currents, turbidity, dissolved oxygen, and the Be-7 activity of particulates in bottom sediments, sediment traps, and suspended particulates have been made over a 3 year period. A tracer of short term particle dynamics, Be-7 (half life 53 d) is useful in estimating particle residence times in the water column, along with episodic sediment deposition and erosion rates, and the average number of deposition/erosion cycles a particle experiences prior to permanent burial in the sediments. Be-7 derived estimates of the age of particulate organic carbon cycling between surface sediments and the overlying waters are on the order of months, and are dependent upon resuspension frequency. Remineralization of organic carbon within this actively resuspended pool of material results in estimated decomposition rates for POC ranging 0.08 to 0.04% per day, a rate intermediate between the rapid remineralization of fresh algal material and post-depositional diagenesis. Comparisons between 1989-90 and 2004-06 show a decrease in resuspension frequency, possibly in response to shifts in regional climatic scale dynamics. This appears to result in an increase in the efficiency of trapping of organic matter in the bay and a significant increase in the organic carbon content of suspended particulates within the resuspension reactor. Measured sedimentation rates determined via Pb-210 and Cs-137 also indicate increased sediment accumulation over this interval. Combined with the wind shift induced reduction in water mass exchange, these climatic changes have the potential to increase hypoxia via enhancing benthic oxygen demand - a common feature of lower Green Bay that recent evidence suggests may be exacerbated, triggering severe oxygen depletion and fish kills.
OS11D-1162
Effect of Changes in Seasonal Rain Regime on Coastal Ecosystem Structure and Aquaculture Activities
A downscaling experiment linked climate forcing produced by a Regional Climate Model for Europe to a 3D high resolution coupled transport biogeochemical model for the Lagoon of Venice, which in turn forced: a) a food web model for evaluation of cascading effects on ecosystem structure and b) a population dynamic bioenergetic filter feeders bivalvae model for evaluation of effects on aquaculture activities. The hierarchy of models was used to compare result for a reference situation (RF, 1961-1990) with results for two future IPCC scenarios (2071-2100), representing market oriented and local sustainability policies (scenarios A2 and B2, respectively). Future climate projections suggest that, locally, annual mean rain will not change much but the seasonal patterns will likely do so. Summer and spring will be more dry and winter and autumn more rainy. This will potentially increase winter nutrient concentrations but -because of unfavourable timing - primary and secondary productions will decrease, and nutrient surplus will be exported from the Lagoon of Venice to the Adriatic Sea. The impacts on higher trophic levels could be softened thanks to presence of alternative energy pathways and role of omnivory. However, in our future scenario of the lagoon food web the suitability for higher trophic level organisms seems lower. A more detailed analysis on clam aquaculture indicates that this activity will suffer the decrease of primary productivity, and point to the need of implementation of proper aquaculture management policies. In the light of adaptive management. These policies cannot be a straightfoward extrapolation of present practises, but need to be defined basing on future conditions.
OS11D-1163
Anthropogenic changes and ecosystem monitoring in the Honjo Area of Nakaumi Lagoon, Southwest Japan
Nakaumi Lagoon is a coastal brackish water lake formed by the Yumigahama peninsula in Shimane and Tottori Prefectures, Southwest Japan. In 1981 the Honjo Area, approximately the northern quarter of Nakaumi Lagoon, was almost completely isolated by the Moriyama and O-misaki Dikes constructed by the Nakaumi Reclamation and Desalination Project. A connection remained with Nakaumi Lagoon via one channel in the West Dike. This channel, 2.3km in length, 75-150m in width, 3m in water depth，prevented the inflow of lagoon water. In 2002, the reclamation project was canceled and restoration work has been undertaken and planned during 2007-2009, such as the opening of 60 meters of the Moriyama Dike and the removal of West Dike. The inflow of high salinity water allowed by this restoration work is expected to have a large impact on the present ecosystem of the Honjo Area. The opening of Moriyama Dike is scheduled for early 2009, and the removal of the West Dike was carried out in July 2007. In this study, we document changes in the water environment resulting from the removal of the West Dike, and discuss probable environmental changes in coastal brackish lagoon systems when Sea level rises in the coming decades. The monitoring program is made up of 60 water quality measurement sites and 12 detailed sampling localities in a traverse line through the lake system and observations were made at monthly intervals from May 2005 to present. At detailed sampling locations we measured standard water quality variables, collected water samples for biomass and stable isotope chemistry, and collected surface sediment samples for geochemistry and benthos censusing. Before the removal of West Dike, surface water salinity in the Honjo Area fluctuated from 12 to 24psu, but the regional difference was very small. After dike removal regional differences in surface salinity gradually increased, with a maximum difference of 11psu across the Honjo Area. Salinity at the mouth of the Honjo Area most likely decreased during times of significant rainfall and runoff into the lake system because of inflow of low salinity Nakaumi surface waters. On the other hand, the salinity difference between surface and bottom water has remained between 2 and 4 psu after the removal of the West Dike except during winter when strong winds mix the Honjo Area waters. For most of the year the water is stratified, and bottom water in the Honjo Area shows oxygen depletion. The dissolved oxygen of bottom water is decreased early in the year in the Moriyama Dike side of the Honjo Area. This oxygen-poor water is easily welled up by winds because the vertical salinity difference is small. At times the observed dissolved oxygen values of surface water is less than 1 mg/l, indicating that the shallow ecosystem is significantly affected. As global temperatures and sea levels rise, similar processes will affect coastal brackish lakes when low-lying sand bars are overridden by seawater. At that time oxygen-poor waters will expand in coastal brackish lakes, and ecosystems will be affected.
OS11D-1164
How do Changes in River Input and Sea Ice Cover Affect the Hudson Strait Outflow?
The waters that flow out through Hudson Strait, a coastal system that connects Hudson Bay with the Labrador Sea, constitute the third largest freshwater contribution to the northern North Atlantic, behind only Fram Strait and Davis Strait. Over the last several decades, large interannual changes have been documented in Hudson Bay, including a decrease in riverine input and a decrease in the length of sea ice coverage. This study examines how these changes impact the structure and variability of the outflow through the strait. Using both recently collected (2004-2006) and historic (1982, 1986-1987) observations obtained from moored and shipboard instrumentation across the outflow, we investigate the connections between the outflow structure and the changing forcing (including riverine, sea ice, and atmospheric) over Hudson Bay. In particular, we focus on the mechanisms that cause the freshwater export to be concentrated to a series of discrete pulses during the fall/winter season. These freshwater pulses, which vary on synoptic timescales, are related to the passage of storms across Hudson Bay, but their structure from year to year also seems to respond to the changing river and sea ice forcing over the region.
OS11D-1165
A regional ocean model for the Pacific Coast of Canada
The Regional Ocean Model System (ROMS) has been implemented for the Canadian Pacific Coast. The relatively high resolution grid (3 km) extends from the Columbia River to the southern Alaskan Coast. This circulation model will ultimately be used to study the impact of climate change on the coastal ocean. Various boundary forcings required to simulate realistic tides as well as seasonal cycle of the water properties (salinity and temperature) and ocean circulation (baroclinic velocity fields as well as longshore transport) have been implemented. Numerical simulations have been performed to reproduce a seasonal cycle of the temperature and salinity fields as well as the longshore circulation. Special attention has been given to the simulation of certain ubiquitous features such as: the seasonal reversal of the shelf break current, seasonal changes in mixed layer depth, upwelling and downwelling transitions in the spring and in the fall, and buoyancy-driven coastal currents.
OS11D-1166
Nearshore Thermal Habitat and General Circulation Mapping in Arctic Alaskan Coasts Using Archived AVHRR Images
At the University of Alaska Fairbanks a continuous archive of images from the Advanced Very High Resolution Radiometer (AVHRR) onboard the series of NOAA satellites is now available starting from 1993 through 2008 for large parts of the circum Arctic north. The largest temporal coverage available is for the Alaskan Arctic coasts and includes over 40000 images for the summer months. The broader objective of our study is to use this wealth of available data for mapping general sea surface temperatures and monitoring trends in changes in the sea surface temperatures in the last 15 years in the Alaskan Arctic Coastal regions. A second objective of our study is to look at near shore circulation patterns, and investigate how changes in the landcover of the adjacent lands affect the nearshore circulation patterns. This information is fundamentally important to understand and predict the dynamics of the shallow coastal habitats that in turn influence the distribution and condition of the fish populations. From the AVHRR archive we extracted all images from the months of July, August and September that covered at least 60 percent of the Arctic Alaskan coastal areas. The images that were in sensor projection were converted to map projection using the coastal boundary vector layer as a guideline for manually selecting tie points to correct for the geometry. Starting from the oldest images in our archive from 1993 we processed over 2000 AVHRR scenes which were then used to generate sea surface temperature images and NDVI images and a time series animation of changing patterns of NDVI. The prototype animation generated to demonstrate the landcover and coastal region dynamics will be further extended to cover the entire time span from 1993 through 2008.
OS11D-1167
Reconstruction of historical estuarine inflows from tidal records.
The historic, pre-development condition of estuaries is of great interest for assessment of climatological and anthropogenic change, and as baseline data for future management. In the Northeast Pacific basin, the historic condition of estuaries is vital for understanding declines in salmonid populations. River inflow has changed due to climate change, as well as flow regulation, irrigation withdrawals, and channel modification. Estimation of historic flows is an important component of the estimation the overall, pre-development state of an estuary. Tidal height records are generally the longest available environmental record for estuarine systems, and frequently pre-date measurements of river flow, at least in the lower (tidal) reaches of major rivers. Thus, tidal records are attractive dataset to use for reconstruction of river flow. The mechanistic connection between river flow and tidal properties is the frictional interaction of flow with the tide – changes in flow change the tidal frequency spectrum (the latter normalized by the tidal potential or data from a nearby coastal station). Standard and robust harmonic analysis methods are used to estimate tidal constituents from the available high-low water records from Astoria, Oregon, USA from 1855 to 1868. Hourly records from 1870-1871 are used to verify tidal predictions from the high-low dataset. Bootstrap error estimation methods, previously applied to regularly-sampled tidal heights, are adapted to calculate confidence intervals for constituents calculated from the irregularly sampled high-low data. Empirical relationships between measured flow and tidal constituents are developed from the 1925-1955 time period. Using these relations, the riverine inflow to the Columbia estuary is estimated for the 1855-1868 time period, including the historic winter and spring floods of 1861-62, both amongst the larger known for the Columbia.
OS11D-1168
High-Resolution Paleosalinity Reconstruction From Laguna de la Leche, North Coastal Cuba, Using Sr, O, and C Isotopes
Isotopes of Sr, O, and C were studied from a 227-cm long sediment core to develop a high-resolution paleosalinity record to investigate the paleohydrology of Laguna de la Leche, north coastal Cuba, during the Middle to Late Holocene. Palynological, plant macrofossil, foraminiferal, ostracode, gastropod, and charophyte data from predominantly euryhaline taxa, coupled with a radiocarbon-based chronology, indicate that the wetland evolved through four phases: (1) an oligohaline lake existed from 6200 to 4800 cal yr B.P.; (2) water level in the lake increased and the system freshened from 4800 to 4200 cal yr B.P.; (3) a mesohaline lagoon replaced the lake 4200 cal yr B.P.; and (4) mangroves enclosed the lagoon beginning 1700 cal yr B.P., forming a mesohaline lake. Isotopic ratios were measured on specimens of the euryhaline foraminifer Ammonia beccarii, although several measurements were also made on other calcareous microfossils in order to identify potential taphonomic and/or vital effects. The 87Sr/86Sr results show that the average salinity of Laguna de la Leche was 1.7 ppt during the early lake phase and 8 ppt during the lagoon phase — a change driven by relative sea level rise. The delta18O results do not record the salinity increase seen in the 87Sr/86Sr data, but instead indicate high evaporation from the lake surface. Variability in delta13C was controlled by plant productivity, episodic marine incursions, and vegetation community change. There is some evidence for seasonal effect and the lateral transport of microfossils prior to burial. Our results show that Sr isotopes, while often cited as a powerful paleosalinity tool, should be used in conjunction with other indicators when investigating paleosalinity trends; relying solely on any single isotopic or ecological indicator can lead to inaccurate results, especially in semi-enclosed and closed hydrological systems.
OS11D-1169
Coastal Algal Blooms in the Southern California Bight
Surface chlorophyll measured at the Scripps Pier in the Southern California Bight (SCB) for eighteen years (1983-2000) reveals that the spring bloom occurs with irregular timing and intensity each year, unlike sea- surface temperature (SST), which is dominated by a regular seasonal cycle. In the 1990's, the spring bloom occurred earlier in the year and with larger amplitudes compared to those of the 1980's. Seasonal anomalies of the chlorophyll have no significant correlation with local winds, offshore winds, or upwelling index anomalies. The annual mean Pier chlorophyll concentration exhibits a clear increasing trend with no concomitant trend evident in the Pier SST over these two decades. The interannual variations of the Pier SST and chlorophyll is not correlated with tropical El Niño or La Niña conditions over the entire observing period, but a few strong El Niño and La Niña events have significant impacts on the Pier data. The Pier chlorophyll is highly coherent at low frequencies (3-7 years) with nearby offshore in situ surface chlorophyll observations at the CalCOFI (California Cooperative Fisheries Investigations) station 93.27. Both the Pier and CalCOFI station 93.27 (12.5 km offshore) are on the continental shelf (water depth<200), but the Pier chlorophyll observations have magnitudes that are roughly one to two orders greater than the offshore surface chlorophyll observed by CalCOFI.