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  • frequencies... Oscillation.
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  • Abstract: The 14C ages of planktonic foraminifers Globigerinoides sacculifer bracketing the Younger Dryas in a d18O record of Globigerinoides ruber from a laminated sediment core on the Pakistani continental margin suggest that surface reservoir ages in the Arabian Sea were in excess of 1000 years during the deglaciation. A least squares error fit of a detailed 14C chronology to the (atmospheric) tree ring record gave variable early Holocene reservoir ages between 780 and 1120 years, well above the prebomb value of 640 years. Mid-Holocene reservoir ages are less well constrained but were probably closer to the prebomb value. The method used to fit individual core sections to the tree ring record was designed to require only a rough a priori estimate of the time spans, which in the core presented here were taken from each section's range of 14C ages. A significant 220-year quasi-oscillation was present in the d18O record during the early Holocene but not thereafter. This frequency and amplitude pattern resembles an early Holocene 207- to 227-year oscillation previously observed in the atmospheric 14C record, which is generally interpreted as reflecting solar irradiance variability. An early Holocene climate event at 8150-8400 calendar years B.P. observed elsewhere within the Asian-East African monsoon system was again found in our record, suggesting a reduction in precipitation over NW India and Pakistan. Category: geoscientificInformation Source: Supplement to: Staubwasser, Michael; Sirocko, Frank; Grootes, Pieter Meiert; Erlenkeuser, Helmut (2002): South Asian monsoon climate change and radiocarbon in the Arabian Sea during early and middle Holocene. Paleoceanography, 17(4), 1063, https://doi.org/10.1029/2000PA000608 Supplemental Information: Selection criteria for core subsections; subsection 4, plateaus in section with discontinuous lamination subsection; subsection 3, between end of continuously laminated sequence and d18O event; subsection 2, between d18O event and onset of continuously laminates sequence; subsection 1, plateau centered around first occurrence of lamination. Coverage: EVENT LABEL: * LATITUDE: 24.610000 * LONGITUDE: 65.982000 * DATE/TIME: 1993-09-15T00:00:00 * ELEVATION: -316.0 m * LOCATION: Arabian Sea * CAMPAIGN: SO90 * BASIS: Sonne * METHOD/DEVICE: Composite Core
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  • Abstract: We have generated 104-year long (1895–1999) monthly d18O and Sr/Ca time series from a fast-growing Diploria strigosa coral core drilled off Guadeloupe Island, Lesser Antilles. Coral Sr/Ca reliably records interannual to decadal surface air temperature (SAT) variations in the region and shows a pronounced warming of approximately 1.5 °C since 1950, with the strongest warming (1.2 °C) occurring since 1975. This warming is also evident in SAT measured at Guadeloupe, which ends in 1951. Thus, our Sr/Ca series extends the air temperature record by 56 years. We find that the past few decades are the warmest years over the entire period of record. The accelerated warming since 1950 is accompanied by a pronounced decrease in regional precipitation. This dampens the warming signal indicated by coral d18O, which is too low (only 0.7–0.8 °C since 1951). Consistently, δ18Osw estimated from the coral proxies also shows a strong decrease since 1950. Our data suggest an inverse relationship between SAT and precipitation (i.e. warmer and drier) for the latter half of the 20th century with the strongest trends since the mid-1970s. This is consistent with recent observational and model data, which report that while over the tropical oceans rainfall has increased due to an increase in sea surface temperatures, precipitation over land regions is reduced. A continuation of this warming and drying trend over Caribbean land regions would have severe societal consequences, especially in the context of anthropogenic warming. The El Niño Southern-Oscillation (ENSO) and the North Atlantic Oscillation (NAO) are the two major climate modes affecting large-scale SST variability in the northern tropical Atlantic. Both Sr/Ca and d18O show a close relationship to ENSO and the NAO. A quantitative comparison between extremes in mean March–May coral d18O and the Nino3 and NAO indices imply that climate variability in the northern tropical Atlantic is mainly forced by tropical Pacific and North Atlantic variability. Spectral analysis suggests that the relative importance of ENSO and the NAO is frequency dependent, with ENSO dominating at interannual, and the NAO dominating at interdecadal time scales. Category: geoscientificInformation Source: Supplement to: Hetzinger, Steffen; Pfeiffer, Miriam; Dullo, Wolf-Christian; Garbe-Schönberg, Carl-Dieter; Halfar, Jochen (2010): Rapid 20th century warming in the Caribbean and impact of remote forcing on climate in the northern tropical Atlantic as recorded in a Guadeloupe coral. Palaeogeography, Palaeoclimatology, Palaeoecology, 296(1-2), 111-124, https://doi.org/10.1016/j.palaeo.2010.06.019 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 16.333330 * LONGITUDE: -61.816660 * DATE/TIME: 2000-04-01T00:00:00 * ELEVATION: 1.7 m * Recovery: 1.26 m * LOCATION: Caribbean * METHOD|DEVICE: Drill, hydraulic
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  • Abstract: Dinocysts from cores collected in the Chukchi Sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques. Holocene sequences have been recovered in a down-slope core (B15: 2135 m, 75°44'N, sedimentation rate of ~1 cm/kyr) and in a shelf core (P1: 201 m, 73°41'N, sedimentation rate of ~22 cm/kyr). The shelf record spanning about 8000 years suggests high-frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar (cal) years B.P. The condensed offshore record (B15) reveals an early postglacial optimum with minimum sea ice cover prior to 12,000 cal years B.P., which corresponds to a terrestrial climate optimum in Bering Sea area. Dinocyst data indicate extensive sea ice cover (>10 months/yr) from 12,000 to 6000 cal years B.P. followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions, superimposed on large-amplitude millennial-scale oscillations. In contrast, d18O data in mesopelagic foraminifers (Neogloboquadrina pachyderma) and benthic foraminifers (Cibicides wuellerstorfi) reveal maximum subsurface temperature and thus maximum inflow of the North Atlantic water around 8000 cal years B.P., followed by a trend toward cooling of the subsurface to bottom water masses. Sea-surface to subsurface conditions estimated from dinocysts and d18O data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate North Atlantic water mass with the existence of a sharp halocline and a reverse thermocline, especially before 6000 years B.P. The overall data and sea ice reconstructions from core B15 are consistent with strong sea ice convergence in the western Arctic during the early Holocene as suggested on the basis of climate model experiments including sea ice dynamics, matching a higher inflow rate of North Atlantic Water. Category: geoscientificInformation Source: Supplement to: de Vernal, Anne; Hillaire-Marcel, Claude; Darby, Dennis A (2005): Variability of sea ice cover in the Chukchi Sea (western Arctic Ocean) during the Holocene. Paleoceanography, 20(4), PA4018, https://doi.org/10.1029/2005PA001157 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 75.733300 * LONGITUDE: -170.000000 * ELEVATION: -2135.0 m * LOCATION: Chukchi Sea * METHOD/DEVICE: Box corer EVENT LABEL: * LATITUDE: 73.683300 * LONGITUDE: -170.000000 * ELEVATION: -201.0 m * LOCATION: Chukchi Sea * METHOD/DEVICE: Box corer EVENT LABEL: * LATITUDE: 73.683300 * LONGITUDE: -170.000000 * ELEVATION: -201.0 m * LOCATION: Chukchi Sea * METHOD/DEVICE: Piston corer
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  • frequency... oscillated
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  • Abstract: Changes in El Niño-Southern Oscillation (ENSO) variability are difficult to extract from paleoceanographic reconstructions because they are superimposed on changes in seasonal variability that modulate the first-order climate signal. Here we address this problem by reconstructing thermocline structure from a marine sediment core retrieved from the eastern equatorial Pacific. At the core location, changes in hydrologic parameters within the thermocline are linked to ENSO activity, with a reduced influence of seasonal variability compared to surface waters. We performed repeated isotopic analyses (d18O) on single specimens of the thermocline-dwelling planktonic foraminifera Neogloboquadrina dutertrei at several targeted time periods over the last 50 ka to extract the total thermocline variance, a parameter supposed to reveal changes in ENSO. No fundamental changes in amplitude and frequency of the events were detected despite differences in climatic background. However, our data suggest that long-term variations in the thermocline variability occurred over the last 50 ka, with the highest and lowest ENSO activities occurring during the last glacial period and the Last Glacial Maximum, respectively. Category: geoscientificInformation Source: Supplement to: Leduc, Guillaume; Vidal, Laurence; Cartapanis, Olivier; Bard, Edouard (2009): Modes of eastern equatorial Pacific thermocline variability: Implications for ENSO dynamics over the last glacial period. Paleoceanography, 24(3), PA3202, https://doi.org/10.1029/2008PA001701 Supplemental Information: Not Availble Coverage: EVENT LABEL: (MD022529) * LATITUDE: 8.205500 * LONGITUDE: -84.122000 * DATE/TIME: 2002-06-23T05:05:00 * ELEVATION: -1619.0 m * Recovery: 35.12 m * LOCATION: Cocos Ridge * CAMPAIGN: MD126 * BASIS: Marion Dufresne (1995) * METHOD/DEVICE: Giant piston corer
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  • Abstract: A multiproxy record has been acquired from a piston core (SO139-74KL) taken offshore southern Sumatra, an area which is situated in the southwestern sector of the tropical Indo-Pacific Warm Pool. The high-resolution data sets (X-ray fluorescence, total organic carbon, and C37 alkenones) were used to track changes in paleoproductivity, freshwater budget, and sea surface temperature (SST) of the tropical climate system at orbital time scales over the past 300 ka. Our paleoclimatic data show that enhanced marine paleoproductivity was directly related to strengthening of coastal upwelling during periods of increased boreal summer insolation and associated SE monsoon strength with a precessional cyclicity. Changes in freshwater supply were primarily forced by precession-controlled changes in boreal NW winter monsoon rainfall enclosing an additional sea level component. SST variations of 2°-5°C occurred at eccentricity and precessional cyclicity. We suggest that the sea surface temperature variability off southern Sumatra is predominantly related to three major causes: (1) variations in upwelling intensity; (2) an elevated freshwater input into the southern Makassar Strait leading to reduced supply of warmer surface waters from the western Pacific and increased subsurface water transport via the Indonesian Throughflow into the Indian Ocean; and (3) long-term changes in the intensity or frequency of low-latitude climate phenomena, such as El Niño-Southern Oscillation. Category: geoscientificInformation Source: Not Available Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: -6.543000 * LONGITUDE: 103.833000 * ELEVATION: -1690.0 m * Recovery: 19.3 m * LOCATION: Indonesia * CAMPAIGN: SO139 * BASIS: Sonne * METHOD/DEVICE: Piston corer (BGR type)
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  • Abstract: Two expeditions to Dorado Outcrop on the eastern flank of the East Pacific Rise and west of the Middle America Trench collected images, video, rocks, and sediment samples and measured temperature and fluid discharge rates to document the physical and biogeochemical characteristics of a regional, low‐temperature (~15 °C) hydrothermal system. Analysis of video and images identified lava morphologies: pillow, lobate, and sheet flows. Glasses from collected lavas were consistent with an off‐axis formation. Hydrothermal discharge generally occurs through pillow lavas but is patchy, sporadic, and sometimes ceases at particular sites of discharge. Yearlong temperature measurements at five of these discharge sites show daily ranges that oscillate with tidal frequencies by 6 °C or more. Instantaneous fluid discharge rates (0.16 to 0.19 L/s) were determined resulting in a calculated discharge of ~200 L/s when integrated over the area defined by the most robust fluid discharge. Such discharge has a power output of 10-12 MW. Hydrothermal seepage through thin sediment adjacent to the outcrop accounts for <3% of this discharge, but seepage may support an oxic sediment column. High extractable Mn concentrations and depleted δ13C in the low but variable organic solid phase suggest that hydrothermal fluids provide a source for manganese accumulation and likely enhance the oxidation of organic carbon. Comparisons of the physical and geochemical characteristics at Dorado and Baby Bare Outcrops, the latter being the only other site of ridge‐flank hydrothermal discharge that has been sampled directly, suggest commonalities and differences that have implications for future discoveries. Category: geoscientificInformation Source: Supplement to: Wheat, C Geoffrey; Hartwell, Anne M; McManus, James; Fisher, Andrew T; Orcutt, Beth N; Schlicht, Lucy E M; Niedenzu, Sara; Bach, Wolfgang (2019): Geology and fluid discharge at Dorado Outcrop, a low temperature ridge-flank hydrothermal system. Geochemistry, Geophysics, Geosystems, 20(1), 487-504, https://doi.org/10.1029/2018GC007933 Supplemental Information: Not Availble Coverage: Not Available
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  • Abstract: Ice-rafting evidence for a '1500-year cycle' sparked considerable debate on millennial-scale climate change and the role of solar variability. Here, we reinterpret the last 70,000 years of the subpolar North Atlantic record, focusing on classic DSDP Site 609, in the context of newly available raw data, the latest radiocarbon calibration (Marine09) and ice core chronology (GICC05), and a wider range of statistical methodologies. A ~1500-year oscillation is primarily limited to the short glacial Stage 4, the age of which is derived solely from an ice flow model (ss09sea), subject to uncertainty, and offset most from the original chronology. Results from the most well-dated, younger interval suggest that the original 1500 ± 500 year cycle may actually be an admixture of the ~1000 and ~2000 cycles that are observed within the Holocene at multiple locations. In Holocene sections these variations are coherent with 14C and 10Be estimates of solar variability. Our new results suggest that the '1500-year cycle' may be a transient phenomenon whose origin could be due, for example, to ice sheet boundary conditions for the interval in which it is observed. We therefore question whether it is necessary to invoke such exotic explanations as heterodyne frequencies or combination tones to explain a phenomenon of such fleeting occurrence that is potentially an artifact of arithmetic averaging. Category: geoscientificInformation Source: Supplement to: Obrochta, Stephen P; Miyahara, Hiroko; Yokoyama, Yusuke; Crowley, Thomas J (2012): A re-examination of evidence for the North Atlantic “1500-year cycle” at Site 609. Quaternary Science Reviews, 55, 23-33, https://doi.org/10.1016/j.quascirev.2012.08.008 Supplemental Information: Not Availble Coverage: Not Available
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  • Abstract: Western subtropical North Atlantic oceanic and atmospheric circulations connect tropical and subpolar climates. Variations in these circulations can generate regional climate anomalies that are not reflected in Northern Hemisphere averages. Assessing the significance of anthropogenic climate change at regional scales requires proxy records that allow recent trends to be interpreted in the context of long-term regional variability. We present reconstructions of Gulf Stream sea surface temperature (SST) and hydrographic variability during the past two millennia based on the magnesium/calcium ratio and oxygen isotopic composition of planktic foraminifera preserved in two western subtropical North Atlantic sediment cores. Reconstructed SST suggests low-frequency variability of ~1°C during an interval that includes the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). A warm interval near 1250 A.D. is distinct from regional and hemispheric temperature, possibly reflecting regional variations in ocean-atmosphere heat flux associated with changes in atmospheric circulation (e.g., the North Atlantic Oscillation) or the Atlantic Meridional Overturning Circulation. Seawater d18O, which is marked by a fresher MCA and a more saline LIA, covaries with meridional migrations of the Atlantic Intertropical Convergence Zone. The northward advection of tropical salinity anomalies by mean surface currents provides a plausible mechanism linking Carolina Slope and tropical Atlantic hydrology. Category: geoscientificInformation Source: Supplement to: Saenger, Casey; Came, Rosemarie E; Oppo, Delia W; Keigwin, Lloyd D; Cohen, Anne L (2011): Regional climate variability in the western subtropical North Atlantic during the past two millennia. Paleoceanography, 26(2), PA2206, https://doi.org/10.1029/2010PA002038 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 32.784000 * LONGITUDE: -76.276000 * ELEVATION: -1895.0 m * LOCATION: North Atlantic * METHOD|DEVICE: MultiCorer EVENT LABEL: * LATITUDE: 32.977000 * LONGITUDE: -76.316000 * ELEVATION: -1205.0 m * LOCATION: North Atlantic * CAMPAIGN: KNR140 * BASIS: Knorr * METHOD|DEVICE: Giant gravity corer
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