Merging late Holocene molecular organic and foraminiferal-based geochemical records of sea surface temperature in the Gulf of Mexico

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 26 (2011): PA1209, doi:10.1029/2010PA002000.A molecular organic geochemical proxy (TEX86) for sea surface temperature (SST) is compared with a foraminifera-based SST proxy (Mg/Ca) in a decadal-resolution marine sedimentary record spanning the last 1000 years from the Gulf of Mexico. We assess the relative strengths of the organic and inorganic paleoceanographic techniques for reconstructing high-resolution SST variability during recent climate events, including the Little Ice Age (LIA) and the Medieval Warm Period (MWP). SST estimates based on the molecular organic proxy TEX86 show a similar magnitude and pattern of SST variability to foraminiferal Mg/Ca-SST estimates but with some important differences. For instance, both proxies show a cooling (1°C–2°C) of Gulf of Mexico SSTs during the LIA. During the MWP, however, Mg/Ca-SSTs are similar to near-modern SSTs, while TEX86 indicates SSTs that were cooler than modern. Using the respective SST calibrations for each proxy results in TEX86-SST estimates that are 2°C–4°C warmer than Mg/Ca-SST throughout the 1000 year record. We interpret the TEX86-SST as a summer-weighted SST signal from the upper mixed layer, whereas the Mg/Ca-SST better reflects the mean annual SST. Downcore differences in the SST estimates between the two proxies (ΔT = TEX86 − Mg/Ca) are interpreted in the context of varying seasonality and/or changing water column temperature gradients.This work was supported, in part, by the National Science Foundation under grants OCE‐0318361 and OCE‐0903017

Remote and local drivers of Pleistocene South Asian summer monsoon precipitation: A test for future predictions

South Asian precipitation amount and extreme variability are predicted to increase due to thermodynamic effects of increased 21st-century greenhouse gases, accompanied by an increased supply of moisture from the southern hemisphere Indian Ocean. We reconstructed South Asian summer-monsoon precipitation and runoff into the Bay of Bengal to assess the extent to which these factors also operated in the Pleistocene, a time of large-scale natural changes in carbon dioxide and ice volume. South Asian precipitation and runoff are strongly coherent with, and lag, atmospheric CO2 changes at Earth-orbital eccentricity, obliquity, and precession bands and are closely tied to cross-equatorial wind strength at the precession band. We find that the projected monsoon response to ongoing, rapid high-latitude ice melt and rising CO2 levels is fully consistent with dynamics of the past 0.9 million years

Late Holocene Climate Variability From Northern Gulf of Mexico Sediments: Merging Inorganic and Molecular Organic Geochemical Proxies

Accurate reconstruction of natural climate variability over the past millennium is critical for predicting responses to future climate change. In order to improve on current understanding of climate variability in the sub-tropical North Atlantic region over the past millennium, a rigorous study of Gulf of Mexico (GOM) sea surface temperature (SST) variability was conducted using both inorganic (foraminiferal Mg/Ca) and molecular organic (TEX86) geochemical proxies. In addition to generating multiple high-resolution climate records, the uncertainties of the SST proxies are rigorously assessed. There are 3 major research questions addressed: (1) What was the magnitude of GOM SST variability during the past 1,000 years, particularly during large-scale climate events such as the Little Ice Age (LIA) and the Medieval Warm Period (MWP). (2) Is the SST signal reproducible within the same sediment core, among different northern GOM basins, and using different geochemical SST proxies? (3) What are the ecological controls on the paleothermometers used to reconstruct SST variability in the GOM? Can differences in the ecology (i.e. seasonal distribution, depth habitat, etc.) of distinct paleothermometers be exploited to gain insight into changes in upper water column structure or seasonality in the GOM during the LIA and MWP? The major findings include: (1) The magnitude of temperature variability in the GOM over the past millennium is much larger than that estimated from Northern Hemisphere temperature reconstructions. The MWP (1400-900 yrs BP) was characterized by SSTs in the GOM that were similar to the modern SST, while the LIA (400-150 yrs BP) was marked by a series of multidecadal intervals that were 2-2.5°C cooler than modern. (2) This LIA cooling was replicated in the Mg/Ca-SST records from three different well-dated northern GOM basins (Pigmy, Garrison and Fisk Basins), as well as in two different geochemical proxies. (3) It is determined that foraminiferal test size has a significant effect on shell geochemistry. Using core-top calibration, discrepancies in the seasonal/depth habitats between different planktonic Foraminifera, and between Foraminifera and Crenarchaeota are inferred. Downcore differences are used to make inferences about changes in GOM mixed layer depth and seasonality over the past millennium

A 1400-year multi-proxy record of climate variability from the northern Gulf of Mexico

A continuous, decadal-scale resolution multi-proxy record of climate variability over the past 1400 years in the northern Gulf of Mexico (GOM) was constructed from a box core recovered in the Pigmy Basin. Proxies include paired analyses of Mg/Ca and oxygen isotopes in the white variety of the planktic foraminifer Globigerinoides ruber and relative abundance variations of G. sacculifer in the foraminifer assemblages. Two multi-decadal intervals of sustained high Mg/Ca values indicate GOM sea-surface temperatures (SSTs) were as warm or warmer than near-modern conditions between 1000 and 1400 yrs BP. Foraminiferal Mg/Ca values during the coolest interval of the Little Ice Age (ca. 250 yrs BP) indicate that SST was 2 - 2.5 degrees Celcius below modern SST. Four minima in the Mg/Ca record between 900 and 250 yrs BP correspond with the Maunder, Spörer, Wolf and Oort sunspot minima, suggesting a link between solar insolation and SST variability in the GOM. An abrupt shift recorded in both the oxygen isotopic ratio of calcite and relative abundance of G. sacculifer occurs ~600 yrs BP. The shift in the Pigmy Basin record corresponds with a shift in the sea-salt-sodium (ssNa) record from the GISP2 ice core, linking changes in high-latitude atmospheric circulation with the subtropical Atlantic Ocean

Late Holocene Climate Variability From Northern Gulf of Mexico Sediments: Merging Inorganic and Molecular Organic Geochemical Proxies

Accurate reconstruction of natural climate variability over the past millennium is critical for predicting responses to future climate change. In order to improve on current understanding of climate variability in the sub-tropical North Atlantic region over the past millennium, a rigorous study of Gulf of Mexico (GOM) sea surface temperature (SST) variability was conducted using both inorganic (foraminiferal Mg/Ca) and molecular organic (TEX86) geochemical proxies. In addition to generating multiple high-resolution climate records, the uncertainties of the SST proxies are rigorously assessed. There are 3 major research questions addressed: (1) What was the magnitude of GOM SST variability during the past 1,000 years, particularly during large-scale climate events such as the Little Ice Age (LIA) and the Medieval Warm Period (MWP). (2) Is the SST signal reproducible within the same sediment core, among different northern GOM basins, and using different geochemical SST proxies? (3) What are the ecological controls on the paleothermometers used to reconstruct SST variability in the GOM? Can differences in the ecology (i.e. seasonal distribution, depth habitat, etc.) of distinct paleothermometers be exploited to gain insight into changes in upper water column structure or seasonality in the GOM during the LIA and MWP? The major findings include: (1) The magnitude of temperature variability in the GOM over the past millennium is much larger than that estimated from Northern Hemisphere temperature reconstructions. The MWP (1400-900 yrs BP) was characterized by SSTs in the GOM that were similar to the modern SST, while the LIA (400-150 yrs BP) was marked by a series of multidecadal intervals that were 2-2.5°C cooler than modern. (2) This LIA cooling was replicated in the Mg/Ca-SST records from three different well-dated northern GOM basins (Pigmy, Garrison and Fisk Basins), as well as in two different geochemical proxies. (3) It is determined that foraminiferal test size has a significant effect on shell geochemistry. Using core-top calibration, discrepancies in the seasonal/depth habitats between different planktonic Foraminifera, and between Foraminifera and Crenarchaeota are inferred. Downcore differences are used to make inferences about changes in GOM mixed layer depth and seasonality over the past millennium

GDGT and alkenone flux in the northern Gulf of Mexico: Implications for the TEX 86 and U K' 37 paleothermometers

The TEX86 and U-37(K') molecular biomarker proxies have been broadly applied in downcore marine sediments to reconstruct past sea surface temperature (SST). Although both TEX86 and U-37(K') have been interpreted as proxies for mean annual SST throughout the global ocean, regional studies of glycerol dibiphytanyl glycerol tetraethers (GDGTs) and alkenones in sinking particles are required to understand the influence of seasonality, depth distribution, and diagenesis on downcore variability. We measure GDGT and alkenone flux, as well as the TEX86 and U-37(K') indices in a 4 year sediment trap time series (2010-2014) in the northern Gulf of Mexico (nGoM), and compare these data with core-top sediments at the same location. GDGT and alkenone fluxes do not show a consistent seasonal cycle; however, the largest flux peaks for both occurs in winter. U-37(K') covaries with SST over the 4 year sampling interval, but the U-37(K') SST relationship in this data set implies a smaller slope or nonlinearity at high temperatures when compared with existing calibrations. Furthermore, the flux-weighted U-37(K') value from sinking particles is significantly lower than that of underlying core-top sediments, suggesting preferential diagenetic loss of the tri-unsaturated alkenone in sediments. TEX86 does not covary with SST, suggesting production in the subsurface upper water column. The flux-weighted mean TEX86 matches that of core-top sediments, confirming that TEX86 in the nGoM reflects local planktonic production rather than allochthonous or in situ sedimentary production. We explore potential sources of uncertainty in both proxies in the nGoM but demonstrate that they show nearly identical trends in twentieth century SST, despite these factors.USGS Climate and Land Use Research and Development Program6 month embargo; First published: 19 December 2016This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Record of d2H of dinosterol variability in down core lake sediments from Clear Lake, Palau

Dataset: Clear Lake 800-yr reconstructionRecord of d2H of dinosterol variability in down core lake sediments from Clear Lake, Palau. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/699469NSF Division of Ocean Sciences (NSF OCE) OCE-124124

Northwestern Gulf of Mexico Holocene G. ruber geochemistry from 2010-GB2-GC1

This dataset contains stable oxygen isotope, radiocarbon, and magnesium-to-calcium ratios measured in G. ruber (white) from a core in the northwestern Gulf of Mexico (Garrison Basin). The dataset also contains the inverted temperature, δ¹⁸O-sw (ice-volume corrected), and salinity values using the PSU Solver Algorithm. A Holocene composite of these parameters is provided for the Garrison Basin with higher-resolution (and previously published) late Holocene records from multi-cores. Here is the abstract from the paper: The Gulf of Mexico (GoM) is an integral component of oceanic circulation in the North Atlantic and helps facilitate poleward heat transport in the Western Hemisphere. Regionally, it serves as a key source of moisture for much of North America. Modern patterns of sea-surface temperature (SST) and salinity in the GoM are influenced by the Loop Current, its eddy-shedding dynamics, and the ensuing interplay with coastal processes. Here we present sub-centennial-scale records of SST and the stable oxygen isotope composition of seawater (δ¹⁸Osw; a proxy for changes in salinity) over the past 11,700 years using planktic foraminiferal geochemistry in sediments from the Garrison Basin, northwestern GoM. We measured δ¹⁸O and magnesium-to-calcium ratios in tests of Globigerinoides ruber (white variety) to generate quantitative estimates of past sea-surface conditions. Our results replicate and extend late Holocene reconstructions from the Garrison Basin, which we then use to create Holocene composites of SST and δ¹⁸Osw. We find considerable centennial and millennial-scale variability in both SST and δ¹⁸Osw, although their evolution over the Holocene is distinct. Whereas mean-annual SSTs display pronounced millennial-scale variability, δ¹⁸Osw exhibits a secular trend spanning multiple millennia and indicates increasing sea-surface salinity in the northwestern GoM since the early Holocene. We then synthesize available Holocene records from across the GoM, and alongside the Garrison Basin composite, uncover substantial, yet regionally consistent, spatiotemporal variability. Finally, we discuss the role of the Loop Current and coastal influx of freshwater in imposing these heterogeneities and conclude that dynamic and variable surface-ocean changes occurred across the GoM over the Holocene