<p> Recent research has proposed that an increase in sea surface temperatures (SSTs) interpreted to be caused by anthropogenic climate change has lead to an increase in the frequency of intense hurricanes. However, this theory has been challenged on the basis that the instrumental record is too short (approximately 160 years) and unreliable to reveal any long-term trends in intense hurricane activity. This limitation can be addressed by the means of paleotempestology, a field that studies past hurricane activity by means of geological and biological proxy techniques. Hurricane-induced overwash deposits that become preserved in the sediments of back-barrier lagoons, lakes and marshes can provide scientists a unique opportunity to study past hurricane landfalls. It also provides an opportunity to study their associated climate drivers over much longer time-scales (centuries to millennia). </p><p> This study investigates overwash deposits (paleo-tempestites) at 10 sites along the Southwest Florida coastline, focusing on two. The Sanibel Island marsh and Keewaydin Island lagoon have a high potential for recording hurricane-induced paleo-tempestites. The Sanibel Island marsh record was constructed using loss-on-ignition, grain size analysis, percent calcium carbonate, and chronologically dated using 210Pb analysis. Proxy and dating results of three sediment cores revealed two prominent paleo-tempestites&mdash;likely representing Hurricane Donna (1960) and the Great Miami Hurricane of 1926. These layers were deposited as both fine-grained sand and shell hash, and contribute to our understanding of storm overwash in the modern record. Three sediment cores were also extracted from a back-barrier lagoon (Island Bay), behind Keewaydin Island in Collier County, Florida. Core samples were analyzed for grain size, percent calcium carbonate, fossil shells species and dated using the ²¹⁰Pb and ¹⁴C dating methods. These methods revealed a 1 thousand year old record of hurricane overwash. Two prominent paleo-tempestites, deposited as both fine-grained sand and shell hash, were also observed at this site and may possibly replicate the most recent storm events documented on Sanibel Island. This suggests that only the most intense hurricanes are being recorded in the geologic record. </p><p> "Active" (1000-500 yrs. BP) and "inactive" (500-0 yrs. BP) periods of hurricane overwash were identified in the Island Bay record. These correlate well with the reconstructed SSTs from the Main Development Region in the North Atlantic Ocean during the Medieval Warm Period and Little Ice Age. Results from this initial Southwest Florida study point to SSTs of the North Atlantic Main Development Region as a potential climatic driver of hurricane landfalls in Southwest Florida over the past 1 thousand years. This is in opposition to SSTs in the Gulf of Mexico and El Ni&ntilde;o Southern Oscillation as hypothesized by other studies in the Gulf of Mexico and Caribbean regions. These results are the first proxy records of past hurricane strikes in Southwest Florida. </p>

<p> A sediment core from Clear Lake, CA that was drilled in 2012 is the centerpiece of a current interdisciplinary paleoclimate investigation in northern California. Two similar research projects were conducted in Clear Lake in 1973 and 1980, but inconsistent core recovery and a possible hiatus in sedimentation introduced uncertainty about the length of time represented by recovered sediments. Two cores recovered in 2012 were drilled in effort to create a continuous splice and attain a complete paleoenvironmental record for the Clear Lake area. Until now, the core has been radiocarbon dated to about 55 meters below lake floor (mblf) and one ash has been identified at 63 mblf, but the lower 90 meters of sediment remained undated. </p><p> Paleomagnetic research provides a chronostratigraphic framework for the collaborative project and reveals variations in sediment flux and environmental conditions over time. In Clear Lake sediments, magnetic minerals are ubiquitous and demonstrate reliable magnetic behavior for magnetostratigraphic interpretation, such as relative paleointensity (RPI) correlation. RPI correlation provides continuous chronostratigraphy for the core to 108 mblf, which corresponds to more than 200 ka. </p><p> Magnetic mineral concentration and grain domain size of Clear Lake sediments reflect zones of varying environmental conditions within the watershed that correlate with previous pollen research. These zones can be correlated to select Marine Isotope Stages (MIS), providing a direct link between paleoclimatic conditions in the marine and terrestrial environment in California. The boundary of MIS 1 and MIS 2, known to occur at 14 ka, is clearly shown as an increase in magnetic mineral concentrations responding to wetter conditions in MIS 2. These results are consistent with previous palynological interpretations from Clear Lake [Adam and Robinson, 1988]. Magnetic mineral concentrations reflect five zones of distinct environmental conditions and also suggests that sedimentation rate increases dramatically in the lower 30-40 meters of the core. </p><p> <b>The environmental magnetic response of Clear Lake sediments, in conjunction with a magnetostratigraphic interpretation, provides a unique opportunity to investigate the timing of environmental change in the lake region.</b> California&rsquo;s current drought may be a new norm of extreme weather in response to higher average temperatures associated with climate change, and paleoenvironmental research like this provides insight on whole-system responses to rapid environmental change.</p>

<p> A &sim;2500 year record of hydrologic change from southern Iran is inferred from the mineralogy and stable isotopic composition of bulk and biogenic carbonates archived in Lake Hirom (27&ordm; 57&rsquo;N, 53&ordm;52&rsquo;E). This change is related to regional variations in moisture and to the larger Indian Summer Monsoon circulation (ISM). During the early Holocene, increased summer insolation from ~10,000 to 8,000 yr BP contributed to the intensification of the ISM. This intensification may have increased summer precipitation north of the modern ISM limit. Evidence of wetter lake conditions in Lake Hirom occur from 8,800 to 7,800 yr BP. Drier conditions occur and persist from 7,800 to 6,300 yr BP, until lacustrine marl changes to peat, indicating maximum aridity. The timing of the drying trend in the mid-Holocene of Lake Hirom correlates with cave and lake records in the Arabian Peninsula, and lake records in northern Iran, indicating a regional drying event.</p>

<p> The Paleocene-Eocene Thermal Maximum (PETM) was followed by a lesser hyperthermal event, called ETM2, at &sim;53.7 Ma (Zachos et al., 2010). The carbon isotope excursion and global temperature increases for ETM2 were approximately half those of the PETM (Stap et al., 2010). The paleohydrologic response to this event in the continental interior of western North America is less well understood than the response to PETM warming. Although ETM2 is better known from marine than continental strata, the hyperthermal has been identified from outcrops of the alluvial Willwood Formation from the Deer Creek and Gilmore Hill sections of the McCullough Peaks area in the Bighorn Basin, Wyoming (Abels et al., 2012). The presence of ETM2 in Willwood Formation strata provides a rare opportunity to examine local continental climactic and sedimentary response to this hyperthermal. </p><p> Core drilled at Gilmore Hill was described and analyzed geochemically. The core consists of paleosols formed on mudrocks that are interbedded with siltstones and sandstones. Carbon isotope analysis of carbonate nodules from paleosols in the core shows that the top of the core, below a prominent yellow sandstone, most likely records the very beginning of the carbon isotope excursion that marks ETM2 (Maibauer and Bowen, unpublished data).The rest of the CIE was likely either not recorded due to sandstone deposition or removed by erosion prior to the deposition of the sandstone. </p><p> Analysis of bulk oxides in the paleosols using the methods of Sheldon et al. (2002) and Nordt and Driese (2010b) provides quantitative estimates of precipitation through the core section. The estimates reveal drying over the &sim;15m leading up to ETM2. Red and brown paleosols, attributed to generally dry conditions, dominate the entire section below the onset of ETM2 and confirm drier conditions. In contrast, thick purple paleosols are associated with ETM2 at the Deer Creek site and suggest wetter conditions during most of the ETM2 interval. The prominent yellow sandstone at the top of the Gilmore Hill core was probably deposited during those wetter climate conditions. </p><p> The core displays distinct changes in stratigraphic architecture: the bottom &sim;100m is mudrock-dominated and the top &sim;100m is sandstone dominated. Several PETM studies have suggested that sediment coarsening in continental basins in the US and Spain developed in response to precipitation changes associated with global warming. Analysis of the Gilmore Hill core's stratigraphic architecture in conjunction with carbon isotope and precipitation data shows that the prominent sandstone in the position of ETM2 was not caused by climate change. The sandstone is the uppermost part of the sandstone-rich interval whose base underlies ETM2 by more than 50m. This study shows that the shift from mudrock- to sandstone-dominated stratigraphy at Gilmore Hill, and possibly throughout the McCullough Peaks area, was not caused by climactic change associated with ETM2. While studies of PETM sections have suggested that the hyperthermal caused sediment coarsening in several different basins including the Bighorn Basin (e.g., Schmitz and Pujalte, 2007; Smith et al., 2008b; Foreman et al., 2012), this study suggests that the lesser magnitude ETM2 did not cross the necessary threshold to provoke a sedimentological response in the Bighorn Basin.</p>

<p> Millennial-scale variability in the Indian monsoon was temporally linked to changes in global ocean circulation during the last glacial period, as evidenced by planktic-benthic foraminiferal stable isotope and trace element results from an intermediate depth sediment core from the northwestern Bay of Bengal (Core NGHP-01-19B; 18&deg;58'N, 85&deg;39'E; 1,422 m). Paired planktic foraminiferal Mg/Ca and &delta;¹⁸O_c of <i> G. ruber</i> constrain sea surface temperatures and isolate millennial-scale variations in the &delta;¹⁸O of surface waters (&delta;¹⁸O_sw) which resulted from changes in river runoff in the northwestern Bay. Concurrently with low &delta;¹⁸O_sw events, benthic foraminiferal &delta;¹³C of <i>Cibicidoides </i> spp. decreased, suggesting an increased influence of an aged water mass at this intermediate depth site during the low salinity events. Benthic foraminiferal Cd/Ca of <i>H. elegans</i> supports the identification of this water mass as aged Glacial Antarctic Intermediate Water (GAAIW). Lagged correlation analysis (r= 0.41) indicates that changes in subsurface properties led changes in surface properties by an average of 380 years. The implication is that Southern Hemisphere climate exerted a controlling influence on the Indian monsoon during the last glacial period.</p>

<p> The age of the Ruby Ranch Member (RRM) of the Cedar Mountain Formation in East-Central Utah was recently constrained using carbon isotope chemostratigraphy to span known excursions associated with the late Aptian. The RRM is characterized by calcrete horizons that are thought to occur across the C10 carbon isotope excursion. Along with carbonate stable isotope analyses and the region&rsquo;s paleo-position in a depositional basin on the leeward rain shadow of the Sevier Orogenic belt, this interval is hypothesized to coincide with an aridification event. Our research objective is to quantify the extent of this aridity using clumped isotope paleothermometry (<i>n</i> = 7) and paleoprecipitation proxies (n = 51) for samples collected across the C10 chemostratigraphic interval. Two weathering indices, CIA-K and CALMAG, were applied to data obtained using X-ray fluorescence spectrometry. Using these proxies, we determined mean annual precipitation across the RRM at its type section. Precipitation values (<i> n</i> = 27) obtained through CIA-K for identified paleosol horizons ranged between 795 and 1275 mm/year, and through CALMAG ranged between 735 and 1042 mm/year. Precipitation values decreased through the C10 interval which may indicate increased aridity. Clumped isotopes provided ?47 values ranging from 0.647 to 0.693&permil;. Paleotemperature measurements (n = 4) from accepted carbonate samples were between 27.9 and 46.3 &deg;C. Isotopic compositions of water calculated from carbonates ranged between -4.4&permil; and -1.9&permil; VSMOW. Precipitation values and temperatures were not lowest during the C10 interval. Temperatures peaked at the end of the C10 interval and decreased afterward, indicating a potential for cooler, more arid conditions. These results suggest that carbon cycle changes during the mid-Cretaceous may have influenced paleoclimate conditions experienced in terrestrial settings.</p><p>

<p> Multi-proxy comparative analyses of sediment from Eagle Lake, including TOC, &delta;13C and &delta;15N composition of bulk organic material, n-alkane distribution, and biogenic silica, was used to document hydroclimatic changes during the early and late Holocene. Eagle Lake is currently located near the transition zone of the North American Precipitation Dipole, with the timing of precipitation showing a winter-wet scenario common to the Pacific Northwest, but overall precipitation (e.g. aridity) showing a Pacific Southwest pattern. The width and position of this transition is poorly constrained during the Holocene and is hypothesized to have migrated, particularly in response to the North American Monsoon. Eagle Lake is thus ideal in providing insights to the past positions of the dipole. Multi-proxy analyses results in differences between the early and late Holocene at Eagle Lake. TOC is lower in the early Holocene, however C:N ratios are much more variable indicating a transition from algal source material to terrestrial and back to algal material prior to the Mazama ash. There are also greater fluctuations of biogenic silica during the early Holocene, suggesting rapid changes in productivity. </p><p> To place these Holocene changes within the context of known climatic and anthropogenic conditions of the 20th century, a ~100 year record of hydrologic change is compared to drought and lake-level drops induced by the formation of the Bly Tunnel. Importantly, the effects of the tunnel on lake level is superimposed on the 1930s drought, making it difficult to disentangle the two impacts. However, the TOC and C:N ratios clearly mirror variations in lake level suggesting that they are effective indicators of Holocene variations. </p><p>

<p> Sediment cores from Cascade Lake (68.38&deg;N, 154.60&deg;W) and Shainin Lake (68.34&deg;N, 151.05&deg;W), Arctic Alaska were selected for paleomagnetic analysis to assess 210Pb-14C age control using paleomagnetic secular variation (PSV) and relative paleointensity (RPI) features, and to quantify environmental magnetic variability during the Holocene and late Pleistocene. U-channels were studied through alternating field (AF) demagnetization of the natural remanent magnetization (NRM), and laboratory-induced magnetizations including anhysteretic remanent magnetization (ARM) acquisition, ARM demagnetization, isothermal remanent magnetization (IRM), and hysteresis experiments to determine magnetic mineralogy and grain-size variability. </p><p> Cascade Lake sediment yields a strong, well-defined characteristic remanent magnetization with average maximum angular deviation values of &lt; 2&deg; and average inclinations within 4&deg; of the expected geocentric axial dipole. Correlation of inclination changes with geomagnetic field models, as well as the Burial Lake record ~ 200 km to the west, indicates a variable offset between the Cascade Lake radiometric chronology and the preferred PSV-derived age model (PSV-1), reaching a maximum offset of 1.5&ndash;2.8 kyr during the mid-Holocene. This offset likely results from either a hard-water effect or the incorporation of watershed-stored terrestrial carbon into ¹⁴C samples. The PSV-1 age model extends the Cascade Lake age model to ~ 21 ka. Cascade Lake sediment may be suitable for RPI estimation using the IRM as a normalizer, however three methods of normalization (magnetic susceptibility (kLF), ARM, and IRM) produce similar normalized remanence results. </p><p> Hysteresis experiments and S-ratios for Cascade Lake glacial till and Shainin Lake sediment supports the hypothesis that local bedrock hosts predominantly high-coercivity magnetic material. However, S-ratios from Cascade Lake (~ 21 ka to present) and Shainin Lake (~ 12.6 ka to present) do not appear consistent with Burial Lake S-ratios, and most S-ratio variability is therefore interpreted as a result of site-specific sedimentation processes and background magnetic assemblages. A Younger-Dryas-aged peak in Shainin Lake S-ratios may be revealed by the increased sensitivity of the S-ratio parameter to magnetite at high-coercivity background levels. Cascade Lake S-ratios increase from 10.3 ka to present, potentially indicating Holocene biogenic magnetite production, down-core magnetic dissolution, or eolian input from a fine-grained, low-coercivity magnetic source that is clearly distinct from eolian magnetite at Burial Lake. Anhysteretic susceptibility (k<p style="font-variant: small-caps">ARM</p>)/k<p style="font-variant: small-caps">LF</p> may be a better indicator of this fine-grained magnetite population observed in the north-central Brooks Range, however the origin of this magnetic component remains unclear. This research highlights the potential advantages of supplementing ¹⁴C dating with additional dating methods, and will benefit from ongoing efforts to improve age control (e.g., cryptotephra exploration) and additional magnetic experiments to constrain the source of fine-grained magnetite.</p>

<p> Petrography and phase equilibria involving the minerals trona (Na₂CO₃&bull;NaHCO₃&bull;2H₂O), nahcolite (NaHCO₃), and shortite (Na₂CO₃&bull;2CaCO₃) from the Eocene Green River Formation provide information on the paleoenvironments that controlled their formation during deposition and diagenesis. Shortite and trona are exclusive to the Wilkins Peak Member (WPM) of the Bridger Basin (BB), WY, whereas nahcolite is the primary Na-carbonate mineral in the contemporaneous Parachute Creek Member of the Piceance Creek Basin (PCB), CO. Trona from the BB and nahcolite from the PCB are stratigraphically associated with oil shale, suggesting deposition in perennial, density stratified saline lakes. Preserved primary textures of trona and nahcolite show that they formed at the air-water interface as microcrystalline chemical muds, which supports the hypothesis that precipitation occurred in contact with the early Eocene atmosphere. New experiments (temperature vs. <i>p</i>CO₂) in the NaHCO₃ -Na₂CO₃-CO₂-H₂O system show that nahcolite forms at a minimal <i>p</i>CO₂ concentration of ~ 680 ppm at 19.5 &deg;C, 1 atm, which is lower than the <i>p</i>CO₂ determined by Eugster (1966) (1330 ppm and 1125 ppm with NaCl added). These new results anchor the minimum <i> p</i>CO₂ of the early Eocene atmosphere at ~ 680 ppm. </p><p> Shortite formed diagenetically during burial in the BB as displacive crystals, fracture fills, and pseudomorphous replacements of a precursor Na-Ca-carbonate in carbonate mudstone and oil shale. Experimental results on the thermal stability of shortite in the Na₂CO₃-CaCO₃-H₂O system show that it forms at temperatures > 55 &deg;C, 1 atm, and 1.1m Na₂CO3 via the reaction: Na₂CO₃&bull;CaCO₃&bull;2H₂O_(pirssonite) + CaCO_3(calcite) = Na₂CO₃&bull;2CaCO_3(shortite) + 2H₂O. The large area over which shortite occurs in the WPM indicates saline pore fluids existed in the buried lacustrine sediments and that, at times, giant Na-CO₃-rich saline alkaline lakes existed in the BB during WPM time. The thermal stability of shortite, coupled with vitrinite reflectance data and inferred regional geothermal gradients, establish that the WPM was buried to depths of ~ 1,500 m and experienced post WPM erosion of ~ 800 m.</p>

The recent, rapid decline in Arctic summer sea ice extent has prompted questions as to the rates and magnitude of previous sea ice decline and the affect of this physical change on ice-related ecosystems. However, satellite data of sea ice only extends back to 1978, and mapped observations of sea ice prior to the 1970s are sparse at best. Inventories of boreal ecosystems are likewise hampered by a paucity of investigations spanning more than the past few decades. Paleoclimate records of sea ice and related primary productivity are thus integral to understanding how sea ice responds to a changing climate. Here I examine modern sedimentation, decadal-scale climate change in the recent past, and centennial- to millennial-scale changes of the past 400 ka using both qualitative and quantitative diatom data in concert with sedimentology and organic geochemistry. Diatom taxonomy and corresponding ecological affinities are compiled in this study and updated for the Bering Sea region and then used as recorders of past climate changes. In recent decades, the Pacific Decadal Oscillation and the strength of the Aleutian Low are reflected by subtle changes in sediment diatom assemblages at the Bering Sea shelf-slope break. Farther back in time, the super-interglacial, marine isotope stage (MIS) 11 (428 to 390 ka), began in Beringia with extreme productivity due to flooding of the Bering Land Bridge. A moisture-driven advance of Beringian glaciers occurred while eustatic sea level was high, and insolation and seasonality both decreased at the global peak of MIS 11. Atlantic/Pacific teleconnections during MIS 11 include a reversal in Bering Strait throughflow at 410 ka and a relationship between North Atlantic Deep Water Formation and Bering Sea productivity. Finally, concentrations of the biomarker-based sea ice proxy, IP25, are compared to sea ice concentration across the Bering and Chukchi seas. Changes in the concentration of IP25 in the sediments may be driven by the length of time that the epontic diatom bloom lasts. When combined with a sediment-based proxy for sea surface temperatures, IP 25 can be used to reconstruct spring ice concentration.