Paleoclimates in Southwestern Tasmania during the Last 13,000 Years

Plant-sociological and climatic classification of the Australian Nothofagus cunninghamii rain forest provides the basis for a new, semiquantitative approach to interpretations of late-Quaternary paleoclimates from four pollen sequences in southwestern Tasmania. Varying proportions of rain-forest pollen types in the records were related to different modern rain-forest alliances and their specifc climatic regimes, such as Eastern Rain Forest, Leatherwood Rain Forest, and sclerophyllous, Subalpine Rain Forest. According to this interpretation, early Holocene climates were characterized by 1,600 mm annual precipitation and 10°C annual temperature, conditions substantially warmer and drier than previously thought. Maximum precipitation levels of 2,500 mm annually were not reached until 8,000 years B.P. A short-term cooling episode between 6,000 and 5,000 years B.P. led to the establishment of modern rain-forest distribution in western Tasmania, characterized either by a precipitation gradient steeper than before, or by greater climatic variability. To interpret paleoclimates from before 12,000 years B. P., when non-arboreal environments dominated in western Tasmanian bollen records, various modern treeless environments were studied in search for analogs. Contrary to earlier interpretations, late-glacial environments were not alpine tundra with a treeline at modern sea level, but steppe, with marshes or shallow lakes instead of the modern lakes. Climate was characterized by 50% less precipitation than today, resulting in substantial summer droughts. To explain such drastic precipitation decrease, the westerlies that dominate Tasmanian climate today must have been shifted polewards. This suggestion is supported by climate models that take Milankovitch-type insolation differences into account as well as sea-surface temperatures. Paleolimnological information based on diatom analyses support the general paleoclimatic reassessment

Continuing upward trend in Mt Read Huon pine ring widths – Temperature or divergence?

To date, no attempt has been made to assess the presence or otherwise of the “Divergence Problem” (DP) in existing multi-millennial Southern Hemisphere tree-ring chronologies. We have updated the iconic Mt Read Huon pine chronology from Tasmania, southeastern Australia, to now include the warmest decade on record, AD 2000–2010, and used the Kalman Filter (KF) to examine it for signs of divergence against four different temperature series available for the region. Ring-width growth for the past two decades is statistically unprecedented for the past 1048 years. Although we have identified a decoupling between temperature and growth in the past two decades, the relationship between some of the temperature records and growth has varied over time since the start of instrumental records. Rather than the special case of ‘divergence’, we have identified a more general time-dependence between growth and temperature over the last 100 years. This time-dependence appears particularly problematic at interdecadal time scales. Due to the time-dependent relationships, and uncertainties related to the climate data, the use of any of the individual temperature series examined here potentially complicates temperature reconstruction. Some of the uncertainty in the climate data may be associated with changing climatic conditions, such as the intensification of the sub-tropical ridge (STR) and its impact on the frequency of anticyclonic conditions over the Mt Read site. Increased growth at the site, particularly in the last decade, over and above what would be expected based on a linear temperature model alone, may be consistent with a number of hypotheses. Existing uncertainties in the climate data need to be resolved and independent physiological information obtained before a range of hypotheses for this increased growth can be effectively evaluated

PICES Press, Vol. 18, No. 2, Summer 2010

•The 2010 Inter-sessional Science Board Meeting: A Note from the Science Board Chairman (pp. 1-3) •2010 Symposium on “Effects of Climate Change on Fish and Fisheries” (pp. 4-11) •2009 Mechanism of North Pacific Low Frequency Variability Workshop (pp. 12-14) •The Fourth China-Japan-Korea GLOBEC/IMBER Symposium (pp. 15-17, 23) •2010 Sendai Ocean Acidification Workshop (pp. 18-19, 31) •2010 Sendai Coupled Climate-to-Fish-to-Fishers Models Workshop (pp. 20-21) •2010 Sendai Salmon Workshop on Climate Change (pp. 22-23) •2010 Sendai Zooplankton Workshop (pp. 24-25, 28) •2010 Sendai Workshop on “Networking across Global Marine Hotspots” (pp. 26-28) •The Ocean, Salmon, Ecology and Forecasting in 2010 (pp. 29, 44) •The State of the Northeast Pacific during the Winter of 2009/2010 (pp. 30-31) •The State of the Western North Pacific in the Second Half of 2009 (pp. 32-33) •The Bering Sea: Current Status and Recent Events (pp. 34-35, 39) •PICES Seafood Safety Project: Guatemala Training Program (pp. 36-39) •The Pacific Ocean Boundary Ecosystem and Climate Study (POBEX) (pp. 40-43) •PICES Calendar (p. 44

A South Polar View of Late Paleozoic Glaciation: Physical Sedimentology and Provenance of Glacial Successions in the Tasmanian and Transantarctic Basins

The Late Paleozoic Ice Age (LPIA; ~ 374 – 256 Ma) is the longest Phanerozoic icehouse interval. this interval in Earth’s history was largely defined by extensive glaciation of the southern hemisphere at both polar and temperate latitudes. Glaciers are powerful climatic and geologic actors, especially during icehouse periods, and widespread glaciation can have a significant influence on both regional and global climate and geology. Therefore, constraining the characteristics of LPIA glaciers is essential to developing a global-scale understanding of this key climatic event in Earth’s history. The manuscripts in this dissertation examine the sedimentology, transport directions, stratigraphy, and detrital zircon provenance of the Pennsylvanian – Permian glacigenic succession from the LPIA at locations in the Transantarctic (Antarctica) and Tasmanian (Australia) basins. The Transantarctic and Tasmanian basins share many characteristics that make them interesting and important places to study LPIA glacigenic rocks. In both basins, sediments were deposited during a ~ 14 Myr icehouse interval spanning the Pennsylvanian-Permian boundary during which time glaciation is thought to have been the most extensive of the LPIA. During this interval, both basins were located at high (\u3e 60˚) southern latitudes along the Panthalassan margin of southeastern Gondwana. The similarities in paleogeographic, geologic, and temporal contexts between the Transantarctic and Tasmanian basins mean that characterizing and comparing LPIA glaciations in both areas is critical to understanding the late Paleozoic glacial maximum at polar latitudes. The works presented in this dissertation demonstrate that building an accurate, nuanced understanding of global glaciations during the LPIA, requires beginning at the local scale and building outward. Chapter 2 examines the Pagoda Formation of the Transantarctic Basin at four locations in the Shackleton Glacier Region of Antarctica. The dominant lithology in the Pagoda Fm at those locations is a massive, sandy, clast-poor diamictite. Depositional processes governing these diamictites were proglacial, subaqueous glacial processes, likely a combination of mass transport, iceberg rain-out, iceberg scouring, plume sedimentation, and subglacial till deposition. Some of the deposits are part of grounding-line fan systems. All glacigenic sediments in the Pagoda Fm at these locations were likely deposited during the retreat phase of a single, up to 90 m thick glacial sequence. Flow directions from these successions support the hypothesis that an ice center was present toward the Panthalassan margin of East Antarctica (Marie Byrd Land) during the LPIA. Chapter 3 describes the basal 415 m of the type section of the Wynyard Formation of the Tasmanian Basin, which outcrops along the coast of northwestern Tasmania. Facies associations in this succession include muddy massive diamictite, sandy massive diamictite, and rhythmically laminated fine-grained facies. Respectively, these sediments were deposited as a grounding-zone wedge, proglacial, proximal grounding line fan or morainal bank, and proglacial, glacier-distal cyclopelites. In this succession, the basal Wynyard Fm was deposited in glacier-proximal to glacier-distal, marine environments on a continental shelf at water depths below storm wave base. All facies associations contain mass transport and turbidite deposits that could have been driven by slope instability due to rapid deposition. The “Wynyard Glacier” was most likely an outlet glacier or ice stream draining a large ice cap or ice sheet. Chapter 4 is a detrital zircon geochronology provenance study of sandstones from the Wynyard Formation. These data represent the first such measurements from the Wynyard Formation anywhere in the basin. With these data, and using a “local first” approach, we demonstrated that all measured detrital zircon dates from the Wynyard Fm can be attributed to zircon sources that occur within 33 km of the sample location along the glacier’s flow path. Therefore, while the detrital zircon provenance signature of the Wynyard Fm also supports the hypothesis that the Wynyard Glacier flowed from south to north, this information does not impart insight into where the ice center was nucleated

Descent toward the icehouse: Eocene sea surface cooling inferred from GDGT distributions

The TEX86 proxy, based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids (GDGTs), is increasingly used to reconstruct sea surface temperature (SST) during the Eocene epoch (56.0–33.9 Ma). Here we compile published TEX86 records, critically reevaluate them in light of new understandings in TEX86 palaeothermometry, and supplement them with new data in order to evaluate long-term temperature trends in the Eocene. We investigate the effect of archaea other than marine Thaumarchaeota upon TEX86 values using the branched-to-isoprenoid tetraether index (BIT), the abundance of GDGT-0 relative to crenarchaeol (%GDGT-0), and the Methane Index (MI). We also introduce a new ratio, % GDGTRS, which may help identify Red Sea-type GDGT distributions in the geological record. Using the offset between TEX86H and TEX86L(ΔH-L) and the ratio between GDGT-2 and GDGT-3 ([2]/[3]), we evaluate different TEX86 calibrations and present the first integrated SST compilation for the Eocene (55 to 34 Ma). Although the available data are still sparse some geographic trends can now be resolved. In the high latitudes (>55°), there was substantial cooling during the Eocene (~6°C). Our compiled record also indicates tropical cooling of ~2.5°C during the same interval. Using an ensemble of climate model simulations that span the Eocene, our results indicate that only a small percentage (~10%) of the reconstructed temperature change can be ascribed to ocean gateway reorganization or paleogeographic change. Collectively, this indicates that atmospheric carbon dioxide (pCO2) was the likely driver of surface water cooling during the descent toward the icehouse

Heterogeneity in global vegetation and terrestrial climate change during the late Eocene to early Oligocene transition

Rapid global cooling at the Eocene – Oligocene Transition (EOT), ~33.9–33.5 Ma, is widely considered to mark the onset of the modern icehouse world. A large and rapid drop in atmospheric pCO2 has been proposed as the driving force behind extinctions in the marine realm and glaciation on Antarctica. However, the global terrestrial response to this cooling is uncertain. Here we present the first global vegetation and terrestrial temperature reconstructions for the EOT. Using an extensive palynological dataset, that has been statistically grouped into palaeo-biomes, we show a more transitional nature of terrestrial climate change by indicating a spatial and temporal heterogeneity of vegetation change at the EOT in both hemispheres. The reconstructed terrestrial temperatures show for many regions a cooling that started well before the EOT and continued into the Early Oligocene. We conclude that the heterogeneous pattern of global vegetation change has been controlled by a combination of multiple forcings, such as tectonics, sea-level fall and long-term decline in greenhouse gas concentrations during the late Eocene to early Oligocene, and does not represent a single response to a rapid decline in atmospheric pCO2 at the EOT