PP53A-01
Solar Periodicities and a Monsoon Climate Phase Recorded at the Latest Miocene to Earliest Pliocene Gray Fossil Site, Northeastern TN, USA.
The latest Miocene to earliest Pliocene Gray Fossil Site (GFS) represents a paleosinkhole lake fill located in northeastern TN, USA that includes an exceptionally well-preserved record of sedimentation. The uppermost 2.8 m of lacustrine stratigraphy is characterized by rhythmites that regularly alternate between coarse-grained and organic-rich (A) laminae and fine-grained, silty clay (B) laminae. Both the (A) and (B) components are almost exclusively comprised of clastic materials. In a small, meromictic lake, the presence of laterally continuous laminated sediment that includes well-known solar periodicities in rhythmite thickness at periods of 24 (Hale cycle) and 12 (sunspot cycle) is interpreted as representing annually generated varves that correspond to seasonal variations in sedimentation. The distinctly larger fraction of medium sand-size quartz grains present dominantly within the (A) laminae, as well as the abrupt transitions between (A) and (B) components suggest that the rhythmites represent deposition during alternating high-energy and lower-energy seasons, which are consistent with a monsoonal precipitation pattern. The monsoon climate may relate to changes in the ocean circulation pattern prior to 4.6 Ma that resulted in an increased temperature and atmospheric pressure gradient between the east coast of North America and the Atlantic Ocean. Sediments underlying the 2.8 m varved sequence are characterized by a different sedimentation style comprised of thick successions of individual graded beds with low %OC and less negative stable C isotope values, which collectively suggest that the underlying sediments were likely deposited in a dryer climate phase with reduced vegetative cover. The transition from the underlying sediment to monsoon generated varves is conformable and is consistent with the expansion of a monsoon climate pattern into the GFS watershed.
PP53A-02
Relationship of Pleistocene Cave Sediments to Faunal Palaeoclimate Indicators: Pilot Study at Mt Etna, Queensland
Sediments occur within almost every cave system, but few studies have focused on retrieval of palaeoclimate information from those cave sediments. Exogenetic sediments, those derived from external sources and transported into the cave, could contain valuable indicators of surrounding climate. For example, previous studies have shown a relationship between the mineralogy of clays produced by weathering in different climatic regimes (i.e., illite and chlorite generally reflect weathering in cool and dry conditions, whereas kaolinite and smectite generally reflect chemical weathering in humid and warm settings). We carried out a preliminary case study on Pleistocene cave fills at Mt Etna, Queensland to test the hypothesis that the sediments record ambient weathering profiles and can therefore be used as palaeoclimatic indicators. Caves in this area occur within highly fractured and recrystallised limestone olistoliths that contain siliciclastic strata in places and are bound partly by serpentinites. We compared the clay mineralogy of cave sediments that contain: 1) rainforest vertebrate faunas and 2) more arid, open vertebrate faunas. We also compared sediments in varying positions relative to a sequence of five flowstones. In each case, sediments showed no bedforms and were limited to very fine grained detritus and were therefore interpreted as having been deposited from suspension. Visible bone and flowstone fragments were removed from samples prior to X-ray diffraction, major element and rare earth element (REE) analysis. Samples were also viewed using a scanning electron microscope (SEM). Preliminary results show no apparent difference in clay species in sediments containing rainforest and more arid vertebrate assemblages. Additionally, clay composition did not vary stratigraphically in relation to the positions of flowstone sequences. All samples contain mixtures of illite, kaolinite, smectite and mixed layer illite/smectite. Clays observed using SEM appear to be poorly crystalline suggesting an exogenetic origin. Investigation of rare earth elements of the clays are currently under way because it has been shown previously that endogenetic clays are characterised by light REE depletion with respect to heavy REE. The following hypotheses are being considered to explain the uniformity of clays in the deposits. 1) Changing climate regime did not affect the primary types of clays produced by weathering at Mt Etna. 2) The clays at Mt Etna largely represent endogenetic sources being liberated internally through limestone dissolution. 3) The local karst environment provided a relatively uniform local climate regime, whereas the vertebrate faunas sampled a broader geographic area with less uniform climate. 4) Clays were diagenetically homogenised secondarily within the cave setting.
PP53A-03
Relevance of Palynological Data for Reconstruction of Abrupt Climatic Change in the Neotropics Region, Based on Marine Sediments from the Cariaco Basin, Caribbean Sea
Pollen analyses from a deep marine core from the anoxic Cariaco Basin, off the coast of Venezuela, encompass the Late Glacial/Bolling-Allerod transition, through the Younger Dryas and into the beginning of the Preboreal. The unique pollen assemblages indicate significant differences, as well as some basic similarities, with pollen results from continental cross-sections and lacustrine deposits of Neotropical regions. Interpretation of the pollen data from these marine sediments must address the specific challenge of distinguishing the climatic signal from preservation patterns in the marine environment. Because the Cariaco Basin acts as a natural sediment trap for rapidly accumulating sediments of marine and terrestrial origin, it provides an opportunity to compare both signals. The pollen assemblages in the basin mirror the complex altitudinal zonation of the coastal vegetation as well as its dynamics in the marine environment which went through the oxic-anoxic transition. Correlation of the pollen data with percentage of sediment lightness, oxygen isotopes, and titanium/iron concentrations in other Cariaco basin cores, as well as a comparison with vascular plant data, shows that the pollen signal is related to climatic events, rather than to a simple preservation pattern. However, an increase in pollen productivity might not be indicative of climate conditions, but of increased discharge of terrigenous material from the continent. The relative constancy in the pollen list and the gradual change in the percentage of counted palynomorphs and the diversity of pollen assemblages speaks to altitudinal reconstruction of vegetation. Thus, the Montana rain forest predominated over deciduous Montana forest or Paramo elements during Bolling-Allerod time, but didn't replace them. At the end of the Late Glacial and in the middle of Younger Dryas time, seasonally dry forest prevailed. At the end of a Heinrich Event (ca 15,500 cal B.P.), the largest shift in vegetation corresponds to an otherwise dry episode, correlated with a drop in lake-levels in northern South America and to hiatuses in terrestrial sedimentation. Thus, the pollen data reliably correspond to other available proxies, and we can conclude that the Neotropical region was not affected by dramatic cooling at the time of cold North Atlantic episodes, such as the Younger Dryas. Instead, these periods correspond to significant dryness.
PP53A-04
The 8.2 ka event in Southwestern Mexico, what did really happen?
The 8.2 ka cooling event is the most important climate anomaly occurring during the Holocene. First detected in Greenland ice-cores and lasting approximately 160 years, its expression has been detected mostly in the Atlantic Ocean and the Caribbean Sea. However, there is little evidence of the effects that the climate anomaly may have had elsewhere. Here we present a U/Th dated stalagmite from "Cueva del Diablo", Guerrero State (southwestern Mexico) that grew between 11.11 ± 0.32 and 4.5 ± 0.18 ka B.P., has been analyzed for variations in trace elements, Sr/Ca, Mg/Ca, Ba/Ca, U/Ca ratios, δ18O and δ13C with decadal to semi-decadal age resolution depending on the growth rate. A peak in the Sr/Ca and δ13C at the onset of the 8.2 ka event, followed by a hiatus indicates that massive outflow of freshwater to the North Atlantic, resulted in arid conditions for Soutwestern Mexico. These were most likely the result from a southward migration of the ITCZ, and a temporal reorganization of the major features of atmospheric circulation in the area.
PP53A-05
Paleoenvironmental and paleoclimatic investigations on Isla de los Estados, Argentina
The expedition in November-December 2005 to Isla de los Estados (Staten Island) off the southeastern tip of South America was a cooperative venture between Lund University (LU) and Stockholm University (SU) in Sweden and the CADIC-CONICET Institute in Ushuaia, Argentina. The aim of the expedition was threefold: (1) to extend the Swedish paleoclimatic "ATLANTIS"-project (Greenland, Iceland, Faroe Islands, Azores, Grenada, Tristan da Cunha; PI S Björck) to the southern part of the South American continent, (2) to connect earlier glacial and climate history reconstructions from the Antarctic Peninsula to equivalents north of the Drake Passage in southernmost South America, and (3) to complement paleo-information available from the Tierra del Fuego mainland with information from Isla de los Estados. Focus was on two areas in the northern and north-western part of the island, Bahía Colnett and Bahia Crossley. Detailed geomorphologic and stratigraphic mapping of glacial deposits were combined with sampling sediments for OSL dating. To reconstruct the paleoclimatic development of Isla de los Estados since the last ice retreat, four main peat bog/lake sites were cored and sampled. In addition, living trees of Nothofagus and old logs preserved in the peat were sampled for dendrochronological and dendroclimatological studies. Preliminary results show that the deglaciation of the study area occurred before 16500 cal yr BP. Detailed multi- proxy analyses of the four sequences are under way and first results will be presented.
PP53A-06
Late Holocene Multiproxy Record (Palynology, Stable Isotope and Multi-Element Geochemistry) of Lake Santa Maria del Oro, Western Mesoamerica.
We present the palynological, stable isotope and major element (ITRAX X-Ray fluorescence) data from a 850-cm sediment sequence from the deepest part of lake Santa María del Oro (SMO) in order to document changes in the climatic and limnological conditions and in the vegetation for the last ca. 5000 yr. SMO is a crater lake of (750 m asl, 2 km diam.) located in a tropical sub-humid climate (1250 mm/yr, average annual temperature 21° C) at the transition between the temperate central Mexican highlands and the arid northern regions. Tropical deciduous forests which loose their leaves for 8 months in a year and the tropical oak forests are the main plant communities in the lake catchments. The western part of Mesoamerica is the cradle of maize (Zea mays ssp. mays ) agriculture; this region is probably one of the two centers of maize domestication based on the presence of one of its closets wild relative teosinte (Zea mays ssp. parviglumis ). Chronology was established with 8 AMS radiocarbon dates. Sediments are finely laminated, with some intervals dominated by black and brown clayey silt and others by brown clayey silt and calcareous silt. In some levels, laminae are characterized by silts and fine sands. Authigenic carbonate laminations are formed during the summer season, when the highest temperatures are reached in the area. Throughout the pollen analysis, teosinte pollen and maize pollen was recorded. The major element concentration (Ca and Ti) in the bulk sediments was analyzed by ITRAX multi-element scanner and the isotopic data (δ13C and δ18O) in authigenic carbonates by mass spectrometer. Ca and Ti ITRAX intensities were calibrated to mass % by using the linear relationship between ITRAX intensity and mass % obtained through conventional XRF analysis. Preliminary pollen data of SMO sediments indicates abundant pollen of teosinte from ca. 2000 to 100 BC and maize presence at ca. 1300 BC and ca. 900 BC along with high charcoal particle concentrations, suggesting early agricultural activity in the area, being the first record of maize in the western region of Mesoamerica. The phases with higher concentration of Ti are identified as periods of higher inflow into the lake basin (BC 1700-1400, 0- AD 200, AD 900 and AD 1800-1900). Phases of higher evaporative conditions are identify at ca. BC 700, BC 400, AD 400-800 and AD 1900-2003 based on Ca high values and enriched δ18O and δ13C. There exists a negative relationship between Ca and Ti. Evidence of changes in climatic conditions is inferred from the data.
PP53A-07
Little ice age and global warming trends recorded in the late Holocene stalagmite from the Yongcheon lava tube cave in Jeju Island, Korea
Yongcheon Cave is located on Jeju Island, the southernmost part of Korea. The island is under the strong influence of East Asian monsoon climate. The Yongcheon cave which contains numerous carbonate speleothems was the typical lava tube cave that probably formed between 0.2~0.4 Ma ago. A 11cm-long stalagmite, YC-1, was collected in its growth position in 2005. The 210Pb dating results show that the top 0.9cm of YC-1 is less than 100 years old with a growth rate of 0.033mm/yr. Assuming the constant growth rate of the stalagmite with this growth rate, it is estimated that the stalagmite is about 3,300 years old. Currently, about 100 samples were analyzed for 18O and 13C compositions in the upper 1.25cm part with a sampling interval of 0.125mm. The 18O ranges from -7.4 to -5.8 (PDB), and the 13C varies from -8.0 to -1.7 (PDB). Both 18O and 13C values have decreasing trends during the last 60 years, with the decreases of 1.2 and 4 for 18O and 13C, respectively. Carbon isotopic compositions are more enriched in SGL (Zone of spaced growth laminae; ca -2.5, PDB) than DGL (Zone of dense growth laminae; ca -7.5). This indicates that the carbon in SGL was mostly supplied from the overlying carbonate sediments. Also, more depleted carbon isotopic values in DGL should reflect more influence by organic carbon within the overlying vegetation cover and soil. Elemental results show that there are anti-phase correlations between Mg/Ca and Sr/Ca, and between Ba/Ca and P/Ca. The strong increase in Al/Ca ratio in the upper a few mm indicates that significant change occurred in the overlying sediments above the cave during the past 50 years. These preliminary results imply that the stalagmite of the Yongcheon Cave may have been affected by groundwater residence time related to variation of regional precipitation and carbonate dissolution rate. Oxygen isotopic variation of YC-1 in particular, clearly shows the period of the Little Ice Age and coincides with the instrumental records of Northern Hemisphere temperature variation during the last 1,300 years.
PP53A-08
A High Resolution Record of Recent Climate Change From Isla Isabela in the Gulf of California
Here we report on the stable isotopic composition (oxygen and carbon) and pollen content of seasonally laminated lake sediments from Isla Isabela (21°52' N, 105°54' W) to reconstruct the history of recent climate change in northwestern Mexico. Isabela crater lake is located approximately 30km offshore the state of Nayarit, and is in the precipitation region of the Mexican Monsoon (also called North American Monsoon). Work on an initial short core indicates coherent periodicities in δ13C and δ18O of bulk inorganic carbonate throughout the past two centuries. Most notably, strong excursions in δ13C and observable sedimentological changes occur at depths in the core corresponding to the years 1973-74, 1950s, 1860s, 1810s, and 1780s A.D.—recognized periods of historical drought in Mexico. Further downcore work reveals additional periods of reduced water availability that may correspond to variations in the Mexican Monsoon.