Atmospheric variability and precipitation in the Ross Sea region, Antarctica

<p>Understanding how atmospheric variability in the Pacific sector of Antarctica drives precipitation is essential for understanding current and past climate changes on the West Antarctic Ice Sheet and the Ross Ice Shelf. Precipitation plays a key role in the Antarctic climate system (via mass balance of ice sheets) and is necessary for understanding past climates (via snow and ice proxies). However precipitation is difficult to measure and model and its variability in these regions is still not well understood. This thesis compiles three separate but inter-related studies which provide further understanding of the atmospheric variability of the Ross Sea region and its role in driving precipitation. Synoptic classifications over the Southern Ocean in the Pacific sector of Antarctica (50°S–Antarctic coast, 150°E–90°W) are derived from NCEP reanalysis data (1979–2011), producing a set of six synoptic types for the region. These six types describe the atmospheric variability of the Ross and Amundsen Seas region for the past 33 years and show how hemispheric scale circulation patterns such as the El Niño-Southern Oscillation and the Southern Annular Mode are reflected in local precipitation and temperature on the Ross Ice Shelf. The synoptic types also provide understanding of how different source regions and transport pathways can influence precipitation on the Ross Ice Shelf, which is important for the interpretation of climate proxies. Because of the sparseness of in-situ meteorological measurements in Antarctica, many studies (including the two described above) rely on atmospheric reanalyses data. However, assessments of reanalyses precipitation have only been done on annual and longer timescales. An assessment of the ERA-Interim and NCEP-2 reanalyses precipitation data on synoptic timescales is developed using statistical, event-based analysis of snow accumulation data from automatic weather stations around the Ross Ice Shelf. The results show that there are important differences between the two reanalyses products and that ERA-Interim represents precipitation better than NCEP-2 for this region. Stable isotopes in snow (δ¹⁸O and δD) are widely used as temperature proxies, but are also influenced by moisture history, source region conditions, and cloud micro-physical processes. Further understanding of the relative importance of these other factors is provided by modeling the isotopic composition of snow at Roosevelt Island, an ice core site on the Ross Ice Shelf. A Rayleigh fractionation model is used to determine isotope composition on sub-storm (hourly) timescales, and the results are compared to measured isotope composition. The model is able to reproduce the significant variability of measured isotopes and shows the importance of air-mass mixing and moisture trajectories on the isotopic composition of snow at Roosevelt Island. Together, these studies show how synoptic variability influences precipitation on the Ross Ice Shelf and at Roosevelt Island in particular, and they provide a basis for interpreting stable isotopes and other precipitation-based climate proxies in ice cores from the Roosevelt Island site.</p>

Atmospheric variability and precipitation in the Ross Sea region, Antarctica

<p>Understanding how atmospheric variability in the Pacific sector of Antarctica drives precipitation is essential for understanding current and past climate changes on the West Antarctic Ice Sheet and the Ross Ice Shelf. Precipitation plays a key role in the Antarctic climate system (via mass balance of ice sheets) and is necessary for understanding past climates (via snow and ice proxies). However precipitation is difficult to measure and model and its variability in these regions is still not well understood. This thesis compiles three separate but inter-related studies which provide further understanding of the atmospheric variability of the Ross Sea region and its role in driving precipitation. Synoptic classifications over the Southern Ocean in the Pacific sector of Antarctica (50°S–Antarctic coast, 150°E–90°W) are derived from NCEP reanalysis data (1979–2011), producing a set of six synoptic types for the region. These six types describe the atmospheric variability of the Ross and Amundsen Seas region for the past 33 years and show how hemispheric scale circulation patterns such as the El Niño-Southern Oscillation and the Southern Annular Mode are reflected in local precipitation and temperature on the Ross Ice Shelf. The synoptic types also provide understanding of how different source regions and transport pathways can influence precipitation on the Ross Ice Shelf, which is important for the interpretation of climate proxies. Because of the sparseness of in-situ meteorological measurements in Antarctica, many studies (including the two described above) rely on atmospheric reanalyses data. However, assessments of reanalyses precipitation have only been done on annual and longer timescales. An assessment of the ERA-Interim and NCEP-2 reanalyses precipitation data on synoptic timescales is developed using statistical, event-based analysis of snow accumulation data from automatic weather stations around the Ross Ice Shelf. The results show that there are important differences between the two reanalyses products and that ERA-Interim represents precipitation better than NCEP-2 for this region. Stable isotopes in snow (δ¹⁸O and δD) are widely used as temperature proxies, but are also influenced by moisture history, source region conditions, and cloud micro-physical processes. Further understanding of the relative importance of these other factors is provided by modeling the isotopic composition of snow at Roosevelt Island, an ice core site on the Ross Ice Shelf. A Rayleigh fractionation model is used to determine isotope composition on sub-storm (hourly) timescales, and the results are compared to measured isotope composition. The model is able to reproduce the significant variability of measured isotopes and shows the importance of air-mass mixing and moisture trajectories on the isotopic composition of snow at Roosevelt Island. Together, these studies show how synoptic variability influences precipitation on the Ross Ice Shelf and at Roosevelt Island in particular, and they provide a basis for interpreting stable isotopes and other precipitation-based climate proxies in ice cores from the Roosevelt Island site.</p>

Potential of Arabic documentary sources for reconstructing past climate in the western Mediterranean region from AD 680 to 1815

Archival records and historical documents offer direct observation of weather and atmospheric conditions and have the highest temporal and spatial resolution, and precise dating, of the available climate proxies. They also provide information about variables such as temperature, precipitation and climate extremes, as well as floods, droughts and storms. The present work studied Arab-Islamic documentary sources covering the western Mediterranean region (documents written by Arab-Islamic historians that narrate social, political and religious history) available for the period AD 680–1815. They mostly provide information on hydrometeorological events. In Iberia the most intense droughts were reported during AD 747–753, AD 814–822, AD 846–847, AD 867–874 and AD 914–915 and in the Maghreb AD 867–873, AD 898–915, AD 1104–1147, AD 1280–1340 and AD 1720–1815 had prevalent drought conditions. Intense rain episodes are also reported.

A 12,000 Kyr Paleohydroclimate Record in the Southeastern, U.S.A based on Deuterium from Bat Guano

The southeastern United States endures environmental change from human population increase, climate change, and land use alterations creating the need to understand baseline conditions and environmental patterns prior to human impacts. While paleoenvironmental data can be reconstructed from a variety of archives (e.g. lake sediments, tree rings, speleothems), some geographic areas contain fewer of such records. One archive capable of recording moisture regimes and other paleoenvironmental changes over millennia but has received little attention relative to other climate proxies, are bat guano deposits in cave systems. Bat guano deposits are found in many cave environments in the southeastern United States and can be used as an archive of paleoenvironmental data including precipitation, vegetation, and aspects associated with the ecology of bats. Here, we present a 12,000-year record of paleoenvironmental change based on δ2H stable isotopes in a guano core collected from Cave Springs Cave in Alabama, USA. Results suggest distinct shifts in moisture during the lower Holocene/upper Pleistocene (9,551 – 12,131 cal yr BP) (δ2H values -86.82 – -77.70) and during the middle Holocene (3,886 – 9,351 cal yr BP) (δ2H values -125.74 – -80.63), roughly coinciding with the Holocene Climatic Optimum (HCO) time interval (5,000 – 9,000 cal yr BP). During the last 4,000 years, conditions in the region shifted once again in the southeastern United States region. Climate inferences based on guano δ2H are consistent with the role of atmospheric moisture on regional vegetation changes suggested by previous pollen records obtained from lake sediment cores. This study suggests bat guano δ2H may be a reliable method to provide a long-term paleoclimate record.

Climatic Extremes and Human Resilience: An Examination of Two Hydrographic Basins in the Great Basin (northern Nevada, USA)

&lt;p&gt;The purpose of this paper is to look at the prehistoric human settlement patterns in the northern Great Basin of the United States&lt;br&gt;in light of a variety of climate proxies. &amp;#160;The intent is to look at the response of Great Basin hunter-gatherers in response to extreme climatic events. &amp;#160;&lt;br&gt;Focus will be on two US Geological Survey designated hydrographic basins: the Black Rock Basin and&amp;#160;&lt;br&gt;the Truckee Basin. &amp;#160;The Black Rock Basin contains the Quinn River which originates in the Montanna Mountains and terminates into a seasonal lake&lt;br&gt;on the Black Rock playa. &amp;#160;The Truckee Basin contains the Truckee River which flows from Lake Tahoe in the Sierra Nevada range&amp;#160;&lt;br&gt;to the terminal Pyramid Lake. &amp;#160;&lt;/p&gt;&lt;p&gt;Radiocarbon dates from excavated archaeological sites in the two basins are used as a demographic and settlement proxy. &amp;#160;Climate proxies&lt;br&gt;from the two basins include: oxygen isotope data from Pyramid Lake, pollen cores from Mud Meadows spring and Summit Lake, and tree ring&amp;#160;&lt;br&gt;data from the Jackson Mountains.&amp;#160;&lt;/p&gt;&lt;p&gt;Both basins see initial human settlement during the Younger Dryas period, with a growth in population/settlements through 8000 BP. After&lt;br&gt;approximately 7800 BP, there is a paucity of dated sites until approximately 4000 BP. &amp;#160;Whether this is due to the 8.2 kya BP climatic event and/or&lt;br&gt;the Mount Mazama volcanic eruption, is uncertain. &amp;#160;Oxygen isotope data from Pyramid Lake does indicate a period of hyper-aridity throughout the&lt;br&gt;northern Great Basin between ca. 8-4 kya BP. &amp;#160;The aridity declines after 4 kya based on the oxygen isotope data, and settlement in the&amp;#160;&lt;br&gt;two basins increases. &amp;#160;With the onset of the Late Holocene Drought, ca. 2500 BP, population/settlement declines are seen except around&amp;#160;&lt;br&gt;major lakes, north of 42N latitude, and elevations above 2000m. After 2000 BP, population/settlement increases throughout both basins. &amp;#160;Notable&lt;br&gt;increases of population/settlement occurs in the Late Antique Little Ice Age and continues throughout the Medieval Climatic Anomaly (MCA). Environmental proxy data indicates the MCA was a period of extreme aridity in the northern Great Basin. Despite ameorilating conditions in both basins after the MCA and in the Little Ice Age, population/settlement declines after circa 700 BP. &amp;#160; &amp;#160;&lt;/p&gt;

Accurate dating of stalagmites from low seasonal contrast tropical Pacific climate using Sr 2D maps, fabrics and annual hydrological cycles

Tropical Pacific stalagmites are commonly affected by dating uncertainties because of their low U concentration and/or elevated initial 230Th content. This poses problems in establishing reliable trends and periodicities for droughts and pluvial episodes in a region vulnerable to climate change. Here we constrain the chronology of a Cook Islands stalagmite using synchrotron µXRF two-dimensional mapping of Sr concentrations coupled with growth laminae optical imaging constrained by in situ monitoring. Unidimensional LA-ICP-MS-generated Mg, Sr, Ba and Na variability series were anchored to the 2D Sr and optical maps. The annual hydrological significance of Mg, Sr, Ba and Na was tested by principal component analysis, which revealed that Mg and Na are related to dry-season, wind-transported marine aerosols, similar to the host-rock derived Sr and Ba signatures. Trace element annual banding was then used to generate a calendar-year master chronology with a dating uncertainty maximum of ± 15 years over 336 years. Our approach demonstrates that accurate chronologies and coupled hydroclimate proxies can be obtained from speleothems formed in tropical settings where low seasonality and problematic U–Th dating would discourage the use of high-resolution climate proxies datasets.

Simple Statistical Testing on Existing Data of Core 39 KL SO189/2 to Reveal its Correlation Towards Sea Surface Temperature Variation

Several paleotemperature proxies using marine core sediment data have been developed and well-proven, but they need excellent laboratory handling and destructive tools. Spectrophotometer and Multi-Sensor Core Logger (MSCL) is considered rapid and non-destructive tools compared to other climate proxies. This paper enhances the correlation between existing data of spectrophotometer, MSCL, and sea surface temperature (SST) of the sediment core 39 KL from SO189/2 through a statistical test. The dataset is processed using interpolation, Pearson correlation, and K-means clustering. Pearson correlation reveals a strong correlation between spectrophotometer, MSCL, and SST. K-means clustering points out that SST is shifting from relatively colder to warmer. This study also tries to understand the source of four tephra and one terrigenous layer. It can be concluded that the spectrophotometer and MSCL have a positive correlation to SST variation.

Mismatches of scale in the application of paleoclimatic research to Chinese archaeology

Issues surrounding the difficult task of correlating archaeological and climatic trajectories are directly impacting the study of human-environmental interaction in Ancient China. We have chosen to focus on the 4.2 ka BP event due to the widespread belief in recent Chinese archaeological publications that it brought about the collapse of Neolithic cultures in multiple regions of China. Following a literature review concerning the many issues surrounding the reconstruction of the 4.2 ka BP event in East Asia, we present three short case studies from the Lower Yangzi, the Shaanxi loess plateau, and the Central Plains detailing a number of problems with Chinese archaeological attempts at using climate change as a causal mechanism for sociopolitical change. We then focus on a common but highly problematic methodology—the growing use of archaeological data compiled in the Atlas of Chinese Cultural Relics to correlate with climate proxies in order to generate linear, causal models explaining sociopolitical collapse. We follow with an example from Northeast China, where work from the past three decades has provided ample data with which to begin answering these questions in a more productive manner, and end with a set of suggestions for archaeologists and climate scientists going forward.