PP31A-0171
300 Years of Run-off Changes in Subtropical Florida Forced by Solar Irradiance, Hurricanes, and Human Impact
The coastal wetland ecosystems in Florida are highly sensitive to changes in fresh water run-off, and have experienced significant impacts from recent land use and sea level changes. In addition, the fresh water flow is likely influenced by variations in precipitation, which in Florida is partly related to El Nino-Southern Oscillation (ENSO) variability and tropical storm activity. We present a 300- year record of past changes in the hydrological cycle from a subtropical estuary (Rookery Bay) on the western shelf of Florida, Gulf of Mexico. Palynological and sedimentological analyses of a shallow sediment core reveal significant past changes in run-off and wetland development. Radiocarbon dating and first occurrences of exotic plant species provide a core chronology; age at 60 cm depth is approximately AD 1690. The onset and development of human impact in Florida is evident from high influx rates of Ambrosia pollen, which are indicative of land clearance, and reduced abundance of wetland taxa since AD 1900. Sedimentological analysis reveals several phases of high siliciclastic input, which are interpreted as phases with increased run-off, and are confirmed by higher wetland pollen abundance. High run-off phases consistently correlate to multi- decadal maxima in solar activity. Maximal run-off rates after AD 1900 also relate to increased land clearance and drainage, and correspondingly higher impact from hurricane landfalls in SW Florida. The record can help to reconcile different views on the impact of solar irradiance changes in subtropical Florida, as primarily responding to tropical pacific (ENSO) changes or North Atlantic forcing during the Little Ice Age period. In addition, information on pre-impact state of the coastal ecosystems will help wetland restoration efforts.
PP31A-0172
A 2000-year record of temperature and salinity variation in Chesapeake Bay
Paleoclimatic records for the past 2000 years, including the Medieval Warm Period and Little Ice Age, were reconstructed from Marion-Dufresne cores from Chesapeake Bay (eastern North America). Mg/Ca ratios from the ostracode, Loxoconcha, and oxygen isotopes from the benthic foraminfer, Elphidium, are used as proxies of spring temperature and salinity, respectively. In the bay, salinity is directly related to Susquehanna River discharge, itself a function of regional rainfall. Chronology was constrained using radiocarbon dates derived from the mollusk, Mulinia lateralis, and historical pollen records of colonial land clearance. Mg/Ca ratios range from ~12 to 41 mmol/mol resulting in a temperature range of ~4 to 23° C. δ18 O values ranged from ~2.84 to +0.20‰ (VPDB) with a mean value of -1.16‰. Fluctuations in both the Mg/Ca and δ18O records confirm multidecadal climate variability during the Medieval Warm Period and Little Ice Age. These patterns are similar to those seen during 20th century NAO events, suggesting long term NAO climatic forcing for the region. The 20th century temperature and NAO-variability will be discussed in the context the last 2000 years of North Atlantic-wide climate variability.
PP31A-0173
Mid-Holocene South China Sea Paleoceanographic reconstruction using corals from the Northern Philippines coast
South China Sea (SCS) is a pivotal area to understand the past variability of the East Asian Monsoon system, because it is a major moisture source for the Eastern Eurasian continent. High resolution speleothems records as well as sediment cores from inland lake suggested progressive decreased monsoon intensity during the Holocene. Recently, several high-resolution coral-based reconstructions of Holocene paleoclimate have been reported from the northern margin of the SCS, mostly from Hainan Island (e.g Sun et al., 2005). However, no such study has been conducted along the eastern part of the SCS. We studied, therefore, modern and fossil Porites corals using delta 18O from Luzon Island, the Philippines, in order to reconstruct the paleoceanography in the region. As annual extension rates of the samples well exceeded ~5mm/year, coral delta 18O values can be used as a reliable climate proxy for temperature and salinity of the region. Corals from the Philippines with mid- Holocene ages (4.0-6.1ky BP) showed ~0.62 permil higher delta 18O values compared to the modern corals. Similar delta 18O annual variations between the modern and fossil corals suggest that the seasonality variation between the two time periods is negligible. We compared our coral delta 18O records with Hainan island corals, located in the same latitude in the SCS but in the west coast, to examine the relative contributions from changes in temperature and salinity between the modern and mid-Holocene. Two components can be distinguished since Hainan island corals have been measured both delta 18O and Sr/Ca ratios (Yu et al., 2005). The modern delta 18O difference between Luzon and Hainan corals corresponds well with the differences in sea surface temperature (SST: ~2.9 degrees C) between the two regions. Given that the same SST difference had been existed during the Holocene in the two regions, the Luzon Island SST was higher than the modern as much as 1.6 degrees C. Consequently, at least 0.91 permil of delta 18O has to be attributed as the changing seawater isotopes namely seawater off Luzon Island should had been higher than the present. Assuming that SCS has been a major moisture source during the Holocene, coral records evidently captured the signatures of the East Asian Summer Monsoon intensity variations throughout the Holocene has also influence on in the oceanographic conditions of SCS.
PP31A-0174
Extracting a climate signal from the skeletal geochemistry of the Caribbean coral Siderastrea siderea
Generation of century-long, sub-annually resolved time series of climate variability from massive Atlantic corals has proven difficult for a variety of reasons. Here our objective is to first document that robust proxy climate records can be produced from the slow-growing, massive Atlantic coral Siderastrea siderea and then to generate a proxy climate time series from this heretofore underutilized massive coral. We have generated the first sub-annually (bimonthly) resolved, paired δ18O and Sr/Ca time series from the tropical western Atlantic coral, Siderastrea siderea, from Long Reef in the Dry Tortugas, Florida (~24°33'N, 82°53'W). This record contains a 20-year long calibration window (1973-1992) and a 73-year long verification window (1900-1972), which permits both the quantification of the relationship between coral δ18O-SST and Sr/Ca-SST using an augmented, 1° x 1° gridded SST record and the assessment of the stability and fidelity of these relationships. Both geochemical variables are highly correlated with the augmented instrumental SST record through both the calibration and verification period. The skill of this proxy demonstrates its potential as a continuously growing, long-lived recorder of climate variability for the tropical Atlantic and Intra-American Seas. The relatively slow extension rate of the coral (~4.5 mm yr-1) also suggests the potential for long records of climate variability (>200 years) of the region to be extracted from even modest-sized colonies (~1 m in height).
PP31A-0175
Geochemical Signature of Land-based Activities in Caribbean Coral Surface Samples
Anthropogenic threats to the Mesoamerican Caribbean Reef Ecoregion, resulting from increased sedimentation, agrochemical run-off, coastal development, tourism and overfishing, are of great concern for future coral reef health and sustainability. Abundances of trace metal in corals can be used to monitor and identify the impact of land-based activities on the reef itself. In this study we demonstrate that surface coral samples from four sites in the Mesoamerican Caribbean Reef Ecoregion, Turneffe Atoll, Sapodilla Cayes and Honduras Bay Islands (Utila and Cayos Cochinos), yield statistically different chemical signatures due to their water quality and relative distance from pollution sources. Specifically, samples from the Sapodilla Cayes and the Bay Islands of Honduras yield elevated Ba/Ca and Mn/Ca levels, indicative of greater exposure to sediment-laden runoff form the south. In a similar manner, elevated coral Pb/Ca and Zn/Ca, and Sb/Ca and Cu/Ca values can be linked to mining activities and the use of antifouling paints, respectively. In addition, site heterogeneity was investigated by analyzing replicate cores at a single site from different colonies. We show that regional variability within the Sapodilla Cayes Marine Reserve can be explained by relative location and orientation within the reef and distance from the continental shelf. Our results indicate good reproducibility for the majority of trace metals investigated (not including Sr/Ca or Mg/Ca), suggesting that local environmental changes such as seawater chemistry, and not climate, is the dominant influence on the metal/Ca ratios.
PP31A-0176
Geochemical Proxy Records From a Bahamian Sclerosponge: Reconstructing Temperature and Salinity Over the Last 500 Years
Sclerosponges have a demonstrated potential as recorders of environmental and climate conditions in the oceans over a range of depths, and periods of tens to thousands of years. Their slow growth rates, and consequent long records, coupled with the fact that their skeletons calcify in apparent C and O isotopic equilibrium with their surrounding environment, give sclerosponges a clear advantage over corals for paleoenvironmental studies. In this investigation, stable C and O isotopes and minor element ratios (Sr/Ca and Mg/Ca) are presented from a 550+ year old specimen of Ceratoporella nicholsoni, collected from 122m water depth off of Lee Stocking Island in the Bahamas. The record is generated from sub-sampling at 100 micrometer intervals over an 11 cm length of the specimen, yielding 1100 sub-samples at a resolution of ~2 samples per year back to 1405. Using previously established relationships between Sr/Ca, δ18O, temperature, and salinity for this species, it is possible to reconstruct salinity variations in the tropical Atlantic Ocean over this extended time period. As such, this is the first sclerosponge from Exuma Sound to yield a multi-century salinity reconstruction. Between 1400 and 1996, the salinity shows a gradual long term increase of ~.5 psu. Superimposed on this long term trend are larger variations with periodicities between 25 and 66 years. Around 1740, a notable salinity minimum (<36 psu) is attained coincident with one of the coldest intervals of the Little Ice Age (based on constant growth rates calculated from U/Th age estimates and verified by the δ13C Suess effect). Over the last 100 years of the record, the salinity reconstruction from this sclerosponge is similar to previously published data and can be linked to forcing associated with the North Atlantic Oscillation.
PP31A-0177
Seasonality Records From Stable Isotopes and Trace Elements in Mussel and Limpet Shells From Archaeological Sites on Gibraltar
Seasonal resolution climate records from mid and high latitudes would allow investigation of the role of seasonality in controlling mean climate on diverse timescales, and of the evolution of climate systems such as the North Atlantic Oscillation (NAO). But achieving such seasonal resolution is difficult for regions outside the growth range of surface corals. Marine mollusc shells provide a possible archive and contain growth increments varying in scale from tidal to annual. However, finding and dating sequences of marine mollusc shells spanning long periods of time is difficult due to sea-level change and the destructional nature of most coastal environments. In this study, we have made use of the habit of hominins on Gibraltar to collect molluscs for food over at least the last 120 kyr. In archaeological excavations of two caves (Gorham's and Vanguard Caves), mollusc shells were found, in habitation levels and in sediment blown into the caves. Existing 14C, OSL, and U-series chronologies provide a chronological framework for this suite of samples. The species found are predominantly Mytilus (mussels) or Patella (limpets). Gibraltar is an interesting location for paleoclimate reconstruction due to its proximity to the boundary of modern day climate belts but also due to its anthropological and archaeological importance. To gain a quantitative understanding of the local controls on stable isotopes and trace elements within Gibraltarian shells, we have initiated a water-sampling programme; emplaced a temperature and salinity logger near the sampling site; and marked live Patella and Mytilus with fluorescent dye to firmly establish growth rates and controls on chemical composition. We have also conducted stable-isotope and trace-element analysis of modern and fossil Patella and Mytilus shells by micromilling. Recent Patella and Mytilus shells show that the oxygen isotope composition of modern shells allow the accurate reconstruction of the full seasonal range in sea-surface temperature. Analysis of three fossil Mytilus samples contained within a Neanderthal occupation level from approximately 115 kyr show clear annual cycles in δ 18O but with different absolute values. Patella samples have also been analysed from the last glacial and from 800-300B.C. Results allow an assessment of past changes in seasonality and of the utility of this archeological shell material as an archive for past change.
PP31A-0178
Tree-ring Chronologies, Water Scarcity, and Climatic Change in Utah: Applying a Paleoclimatic Perspective to Present-day Drought Problems in the Water-stressed West
Drought is one of the most common and devastating natural disasters worldwide. One area that is particularly prone to periods of drought is the western United States. Water scarcity in the western U.S. has recently received political and popular attention as this part of the world is currently experiencing a multi-year, regional drought. As western states continue to experience population growth and further development of agriculture and industry, it becomes increasingly important to understand natural cycles of drought, especially given recent predictions for increased aridity in the western United States if global temperatures rise according to current expectations. This study uses tree-ring chronologies based on ring-width measurements from Pinus edulis Engelm. (Two-needle pinyon) and Picea engelmannii Parry ex Engelm. (Engelmann spruce) to reconstruct drought patterns in the Uinta Mountains, Utah, a major source area for the Green River, which is the principal tributary of the Colorado River. These chronologies demonstrate that drought in the Uintas has been cyclic over the last several hundred years, and that the 20th Century may have experienced fewer and less severe droughts than in centuries past. In addition, the importance of both storms originating in the Pacific and those related to the summer monsoon is noted. Comparisons are made with other tree-ring chronologies from the western United States to suggest that concurrent, multi-year droughts are a regular feature of climate in the western U.S. Current efforts to incorporate this information into policy-making and planning in Utah are discussed.
PP31A-0179
A Palynological Approach to Reconstruct Climatic and Oceanic Variability off Senegal During the Late Holocene
Pollen and organic-walled dinoflagellate cyst assemblages from core GeoB9503 retrieved from the mud-belt (50 m water depth) off the Senegal River mouth have been analyzed to reconstruct short-term paleo-oceanographic and paleo-environmental changes in tropical NW Africa during the interval from 4200 to 1200 years before present (BP). Our study emphasizes significant coeval changes in continental vegetation and oceanic environmental changes in and off Senegal. The land-sea correlation is further examined by comparison with paleo-sea surface temperature (SST) reconstructions based on alkenones analyses. These multi-proxy analyses reveal short-term land-sea climatic linkages in the western Sahel during the late Holocene. Initial dry conditions were followed by a strong and rapid humidity increase around 2,800 years BP when the environment became enriched in woody plants and plants requiring wet conditions. This interval is also characterized by the occurrence of dinoflagellate cysts of river plume affinity. We interpret these observations as the result of enhanced Senegal River runoff with high terrigenous input into the ocean and the local occurrence of cool and less-saline surface waters suggesting discharge-induced upwelling off the river mouth. After 2,500 years BP, the environment slowly became drier again, as indicated by slight increases in sahelian savanna and desert elements and SST. Around 2200 years BP, strong fluctuations in pollen and dinocyst accumulation rates in conjunction with periodically lowered SSTs, suggest an episodic "flash flood" events. The driest phase developed after about 1,800 years BP characterized by the decrease of arboreal pollen and its replacement by pollen from the Saharan group and occurrence of pollen of Pinus and Olea that have their source areas in North Africa suggesting strong trade winds. Furthermore, maximum SST in our record and high abundances of dinoflagellate cysts of subtropical/tropical affinity, such as Tuberculodinium vancampoae, indicate high nutrient, warm and stratified surface water conditions over the core site.
PP31A-0180
A Multi-Proxy Paleoclimate Record of Rapid Holocene Climate Variability From Northern Greece/Greek Macedonia
A lacustrine sediment core retrieved from Lake Zazari (40.6°N, 21.6°E), northern Greece was analyzed for stable isotopic and geochemical indications of paleohydrologic changes over the last ~7500 years. Significant transitions in proxy data occur at 1280, 2700, 3500, 4230, 5320, and ~6250 years B.P. Abrupt changes and general proxy trends correlate well with multiple marine records from the southeastern Mediterranean, off the coast of Israel (Schilman et al. 2001), as well as to recorded hydrological changes in the Black Sea (Lamy et al. 20006), and with regional terrestrial records from the Ionnina basin (Frogley et el. 2001) during the Holocene. Within the Lake Zazari basin, the beginning of the Mid-Holocene was dry relative to the Early Holocene. The Mid- Holocene witnessed greater maximum isotopic values for biogenic carbonates ~4‰ shift combined with significant peaks in magnetic susceptibility, drastic oscillations in loss-on-ignition data, and abrupt preservation or absence of biogenic carbonates (freshwater ostracod taxa). These indicators reflect periods of rapid climate fluctuations. Periods of maximum aridity occurred from 6250-5950, 5320-4750, and 4050-3500 yrs. B.P. This suggests the mid-Holocene was relatively dry within northern Greece and was further punctuated by arid events at decadal to centennial scales. During the late Holocene, more humid and stable climate conditions are represented by δ18O decreases of nearly 4‰. Furthermore, in the late Holocene, rapid fluctuations between drier periods (1650- 1450 and 600-150 yrs B.P.) and wetter periods (1400-1200 and 950-550 yrs. B.P.) correspond very well with a recent, high-resolution lake isotope record from Turkey (Jones et.al. 2006) and with sea surface temperatures off the coast of Israel (Schilman et al. 2001). This high-resolution multi-proxy record shows convincing evidence of rapid climate oscillations from the Neolithic thru the Modern Age in mainland Greece. There is further evidence for lake-level response during the Little Ice Age and the Medieval Climatic Anomaly. These climatic sequences may have had an influence on the human history and prehistoric societies of this region within the eastern Mediterranean.
PP31A-0181
Low frequency climate variability in the Caribbean: what proxy reconstructions tell us
A number of proxy records document low frequency variability in ocean-atmosphere climate over the past millennia. The latter part of this period coincides with historical observations that reveal warming trends and a 65- 80 year cycle known as the Atlantic Multi-decadal Oscillation (AMO), against which many proxies are calibrated. However there is some divergence amongst these reconstructions. Puerto Rico is situated in a climatically sensitive region where multi-decadal climatic influences are manifest in seasonal hurricane frequency. We have developed a proxy for low frequency climate fluctuations based upon the 18O of speleothem calcite from a cave in Puerto Rico. Our speleothem-based data is shown to be sensitive to regional rainfall and North Atlantic sea surface temperatures. We compare a number of proxy records and find good agreement in the observed period after 1850 during two cycles of the AMO. However the indices diverge significantly over the three previous centuries, implying different sensitivities to climate forcing and changes in the frequency of climate itself.
PP31A-0182
Anthropogenic CO2 in the North Atlantic Subtropical Gyre: Estimates based on benthic foraminiferal δ13C
The fate of anthropogenic CO2 in the ocean-atmosphere system is of critical importance to predictions of future climate change. Modern dissolved inorganic carbon data have been used to quantify anthropogenic inputs of CO2 into the ocean, but this approach is based on a set of complex assumptions and it lacks the time perspective provided by the marine geologic record. We will present evidence for the 13C Suess effect in the North Atlantic subtropical gyre based on benthic foraminiferal ( Cibicidoides floridanus) carbon stable isotope data from the Great Bahama Bank. Four separate time series from water depths 260, 440, 530, and 700 meters show depletions in 13C over the past 200 years. In each case, the depletion is anomalous in the context of the last millennium. The δ13C anomaly decreases as water depth increases, consistent with an atmospheric source. Comparison with a foraminiferal δ13C record from 46°N suggests the δ13C anomaly enters the upper ocean in the isopycnal outcropping region of the North Atlantic and is transported southward to the Great Bahama Bank. Using simple mass balance calculations, we estimate there is approximately 20 to 40 μmol/kg of anthropogenic CO2 at intermediate depths of the subtropical gyre, consistent with estimates based on modern oceanographic data. These results imply that high-resolution, well- dated benthic foraminiferal stable isotope records have the potential to be used as an independent means for constraining the oceanic sink of anthropogenic carbon dioxide.