Paleoceanography and Paleoclimatology Posters
Presiding: T van de Flierdt, Lamont-Doherty Earth Observatory; K Wei, Department of Geosciences, National Taiwan University
PP23B-01 1330h
Modern Foraminiferal Biofacies of the Antarctic Peninsula Continental Margin
The changing climate and receding ice shelves of the Antarctic Peninsula have prompted the use of foraminifera as paleoecologic indicators in this region. These organisms have been widely used as environmental proxies, and their distribution in the Antarctic Peninsula region is greatly affected by glacial influences. This study determined the distribution of modern foraminifera from the Antarctic Peninsula, and their associations to environmental conditions using various statistical routines. Foraminiferal samples from the Antarctic Peninsula were statistically analyzed to show the biofacies of both agglutinated and calcareous taxa. Results of these analyses yielded distinct biofacies boundaries for both groups. Although statistically distinct biofacies boundaries were defined by analyzing agglutinated foraminfera, these boundaries are gradational, and weakly associated with environmental conditions. This reflects the more general requirements of agglutinated taxa described in this study. The biofacies boundaries of calcareous foraminifera are more distinct, and show strong associations with environmental conditions. Close associations to glacial, water mass, productivity, current energy and dissolution of calcium carbonate were identified. Water masses associated with calcareous biofacies include Ice Shelf Water, Weddell Sea Transition Water, and Circumpolar Deep Water. The results of this study outline the usefulness of individual taxa, and foraminiferal assemblages as paleoecologic indicators in this region.
PP23B-02 1330h
Age and Paleoenvironmental Interpretations of Foraminiferal data from the Hornitos Locality, Northern Chile
Marine sediment samples were collected from the coastal cliff exposed at Hornitos (70°53'50" W, 22°17'00" S), northern Chile, and analyzed for foraminifera. The section is equivalent to the Pliocene La Portada Formation. The 25m section was sampled for biostratigraphic control of a major conglomerate event bed and to interpret the paleoenvironmental significance of the section compared to other Neogene marine sediments deposited on the Mejillones Peninsula. The samples were processed for benthic and planktonic foraminifera using standard techniques. Statistical analyses of the benthic foraminiferal data were used to identify biofacies and species assemblages. Planktonic foraminifera were used for age determination of the section. Four biofacies and five species assemblages were identified. Identification of the planktonic species Globigerinoides conglobatus and Neogloboquadrina acostaensis place the section within planktonic foraminifera zones N18-N20 (early to middle Pliocene). The benthic foraminiferal biofacies identified indicate a fall and rise in sea-level comparable to global sea-level curve estimates of the early to middle Pliocene.
PP23B-03 1330h
Grain Size Analysis of Terrigenous Sediments from the SW African Margin
Median grain size of 18 samples from the Ocean Drilling Project (ODP) Leg 175 Site 1085B core are presented as part of a larger multi-proxy study to determine late Pleistocene paleoclimate for the Southwest African Margin. The site is located west of the Orange River. Site 1085 sediments contain a terrigenous component. Grain size is used as an indication of terrigenous sediment pathway (i.e. Orange River and eolian input). The fine fraction was digested in sodium acetate-acetic acid in order to remove calcite and in 30% hydrogen peroxide to remove organics (Jackson 1979). The samples were then analyzed on the Micrometrics SediGraph 5100 to determine median grain size. Our data show a range of median grain sizes from 0.3868Îœm to 1.8928Îœm with a peak between Marine Isotope Stages (MIS) 5 and 6. Similar results are seen between stages 2 and 1 (Shackford et al. 2004). Higher median grain sizes are used as an indication of eolian transport and lower median grain sizes as hemipelagic transport (Stuut, 2002). The data maintain an inverse relationship between median grain size and weight percent sand. Lower weight percent sand suggests increases carbonate dissolution, probably through greater influences from North Atlantic Deep Water (NADW).
PP23B-04 1330h
Rapid Climatic Change at the End of the Last Glacial as Determined from Palynological Analysis of Sediments from the Cariaco Basin, Venezuela
We report the first palynological study of a deep marine sediment core from the anoxic Cariaco Basin, off the coast of Venezuela. The Cariaco Basin acts as a natural sediment trap for rapidly accumulating sediments of marine and terrestrial origin. This situation creates favorable conditions for studying short-term paleoenvironmental change. Our pollen analyses indicate unique pollen assemblages which mirror the complex altitudinal zonation of coastal vegetation and its dynamics. The pollen analyses encompass the interval from 3 to 9 m in core MD03-2620, spanning the Glacial/Holocene transition and including the Younger Dryas and the beginning of the Preboreal. Our data indicate large changes during the time of Heinrich event 1 (ca 16-14 Kyr BP) with high arboreal/nonarboreal pollen ratios (2/8) and a dominance of wormwood changing to a cereals/sedge community. Another characteristic of this interval is the lowest pollen concentration, indicating the coldest and driest observed conditions. The disappearance of mangrove pollen at the time of the coldest episodes provides additional indirect evidence for the deterioration of climate conditions and for a drop in sea level. Maximum forest vegetation is found from the middle of the Bolling/Allerod and the middle of the Younger Dryas. This is followed by a similar, though less intense, interval of cooling between the Younger Dryas and the Preboreal. Variations in both the diversity of species and the pollen concentration correlate well with changes in sediment color and with the marine oxygen isotope record.
PP23B-05 1330h
Tree Rings as Climate Proxies in Susquehanna River Basin Streamflow
Tree rings have been used throughout the world to reconstruct past climate records. However, no attempt has been made to reconstruct streamflow records for the Susquehanna River Basin. Having previously found a statistical relationship between tree rings and streamflow records in the basin, the researchers have refined this relationship and used it to reconstruct streamflow in the basin back to 1700. Tree ring chronologies were obtained from NOAA's Paleoclimatic International Tree Ring Data Bank for the period 1700 to 1981. Streamflow records were obtained from the USGS website for Harrisburg, PA for the period 1891 - 1981. Six tree ring sites (Figure 1) were used to determine the significance using time series and regression analyses. The highest significance was found among the r-values for tree ring located in Salt Springs Park (.587) and from the combination of all six sites (.584). The tree ring sites were lagged so that the streamflow of year 1 produced the tree rings of year 2. Figure 3 shows the correlation between Salt Springs and Harrisburg streamflow using z-scores as the time series. Figure 4 gives the calibration period of the streamflow data. Figure 5 gives the actual reconstruction of the streamflow records. On the graph there are major peaks and valleys indicating major historical events such as floods and droughts. There is also some decadal variability indicated. The reconstructed data for the 1800s indicates that significant trends were occurring throughout the century.
PP23B-06 1330h
Mid-Late Holocene Climate and Ocean Variability Recorded in Laminated Sediments of the Bay of La Paz, Gulf of California.
Alfonso Basin in the Bay of La Paz contains a sedimentary record ideal for paleoclimate studies because regional -and global- scale climate signals are preserved in its laminated sediments. A sequence of these sediments is analysed in order to reconstruct the climatic and oceanographic variability in the southern part of the Gulf of California, and to provide a climate scenario that would reproduce global paleoclimate patterns in the mid-late Holocene. 14C AMS dating performed on three core intervals determine the chronstratigraphic framework for the last 8000 cal yrs BP. The assemblages of radiolarians are examined in order to supply a tool for deciphering paleoceanographic and paleoclimatic conditions. The records suggest that in the period from 7,800 to 2,700 cal yr BP, dry climatic conditions prevailed with high evaporation that promoted the formation of the Gulf of California Water (GCW). In the interval between 2,700 to 450 cal yr BP the environment of the Bay was warm, dominated by the Equatorial Surface Water (ESW). Several significant millenary-scale cooling events were recognized at 6100, 3600, 3000 and 1400 cal yr BP. In addition, magnetic susceptibility measurements reveal significant terrigeneous input at 7900, 5700, 1700 and 1400 cal yr BP. A 2000 year climatic change cycle was identified, associated to changes in solar activity.
PP23B-07 1330h
Twentieth Century Warming in the California Current Decoupled from Typical Decadal Variations
Microfossils of planktonic foraminifera in marine sediments offer one of the few means available to reconstruct changes in hydrographic structure and infer the mechanisms of change in ocean climate. Here, we present a >250-year record of variations in upper ocean structure of the California Current, inferred from the abundances of planktonic foraminifera in annually varved sediments of the Santa Barbara Basin. Temporal variability in foraminiferal abundance follows two main patterns that are reflected in a Principal Components Analysis. The first pattern (PC 1) involves a substantial 20th century increase in the abundance of mostly tropical and subtropical species, beginning around 1925, that indicate a warming of near-surface waters across the annual cycle of isothermal shoaling and deepening. The second pattern (PC 2) involves species with subpolar affinities that probably reflect decadal scale dynamics within the thermocline. There is a clear separation of the two PCs after 1975 that indicates a near surface warming and isothermal deepening that is distinct from all other time periods of the record. This change coincides with the well-known shift that occurred around 1977 in the North Pacific, where an intensification in the Aleutian Low caused a warming and depression of isotherms in the eastern North Pacific, particularly during winter. While hydrographic structure since the mid-1970s is particularly anomalous with respect to decadal changes in previous centuries, the entire CalCOFI program has taken place in a time period with unusually high abundances of tropical and subtropical species that began in the early 20th century. The patterns observed in the 20th century suggest a response of the California Current to atmospheric warming attributed in part to anthropogenic activity.
PP23B-08 1330h
Late Quaternary Sedimentation and Paleoceanography in the Southern Okinawa Trough: A Synthesis of ODP1202 Scientific Results
Ocean Drilling Program Site 1202 was designed to study the sedimentary regimes of the southern Okinawa Trough and the paleoceanographic evolution of the Kuroshio (Black Current) in the northwest Pacific. Towards this end, this article reviews the last results of recent studies of the southern Okinawa Trough and summarizes the principal findings made by shipboard scientists and shore-based post-cruise researchers. Despite its deep penetration to 410 m below sea floor, the drilled sequence records only a short history of the past 68 kyrs mainly due to the high sedimentation rates at this site. The lower section of the cores contains numerous turbidite layers with distinctive, phased sources of sediment supply. The upper 130 m is free of turbidite disturbance and provides a high-resolution record for magnetic, sedimentologic and paleoceanographic studies. Sea level change, consequently the locations of the shorelines, and the sill depth, determined the main features of sediments of the record. Between 30 and 11 ka, when the sea level was low, the sediments came from both East China continent and Taiwan. After 11 ka, Taiwan sources became dominant, meanwhile Kuroshio has entered the Trough. Sea surface temperature rose from ~23oC during the last glacial and deglaciation interval to ~26oC of Holocene. The monotonous Holocene sediment provides a high-resolution, high-quality record f magnetic intensity, which may serve as a good reference for regional and global correlation.
PP23B-09 1330h
An assessment of interactively coupled paleoclimate-vegetation models
Vegetation is a key component of climate models. Failure to include realistic vegetation-climate interactions can cause significant discrepancies in predicted surface temperature and precipitation. In this study, four different vegetation models -- BIOME4, EVE, IBIS and SIVM -- were coupled to the GENESIS2 global climate model and simulations run for four paleoclimatic time periods in the Miocene and late Pleistocene. The simulated vegetation from each model was compared to observed paleo-distributions derived from pollen and plant macrofossils. The BIOME4 model best reproduces the paleovegetation, and analysis suggests that this is at least in part due to its inclusion of parameterizations of fire disturbance and the effects of atmospheric carbon dioxide levels on plant growth. Furthermore, using one model rather than another results in regional temperature differences of up to 4 °C for annual means and 7 °C for seasonal means.