Browsing by Author "Cronin, TM"

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Open Access
Changes in North Atlantic deep-sea temperature during climatic fluctuations of the last 25,000 years based on ostracode Mg/Ca ratios
(Geochemistry, Geophysics, Geosystems, 2000-12-01) Dwyer, GS; Cronin, TM; Baker, PA; Rodriguez-Lazaro, J
© Copyright 2000 by the American Geophysical Union.We reconstructed three time series of last glacial-to-present deep-sea temperature from deep and intermediate water sediment cores from the western North Atlantic using Mg/Ca ratios of benthic ostracode shells. Although the Mg/Ca data show considerable variability ("scatter") that is common to single-shell chemical analyses, comparisons between cores, between core top shells and modern bottom water temperatures (BWT), and comparison to other paleo-BWT proxies, among other factors, suggest that multiple-shell average Mg/Ca ratios provide reliable estimates of BWT history at these sites. The BWT records show not only glacial-to-interglacial variations but also indicate BWT changes during the deglacial and within the Holocene interglacial stage. At the deeper sites (4500- and 3400-m water depth), BWT decreased during the last glacial maximum (LGM), the late Holocene, and possibly during the Younger Dryas. Maximum deep-sea warming occurred during the latest deglacial and early Holocene, when BWT exceeded modern values by as much as 2.5°C. This warming was apparently most intense around 3000 m, the depth of the modern-day core of North Atlantic deep water (NADW). The BWT variations at the deeper water sites are consistent with changes in thermohaline circulation: warmer BWT signifies enhanced NADW influence relative to Antarctic bottom water (AABW). Thus maximum NADW production and associated heat flux likely occurred during the early Holocene and decreased abruptly around 6500 years B.P., a finding that is largely consistent with paleonutrient studies in the deep North Atlantic. BWT changes in intermediate waters (1000-m water depth) of the subtropical gyre roughly parallel the deep BWT variations including dramatic mid-Holocene cooling of around 4°C. Joint consideration of the Mg/Ca-based BWT estimates and benthic oxygen isotopes suggests that the cooling was accompanied by a decrease in salinity at this site. Subsequently, intermediate waters warmed to modern values that match those of the early Holocene maximum of ∼7°C. Intermediate water BWT changes must also be driven by changes in ocean circulation. These results thus provide independent evidence that supports the hypothesis that deep-ocean circulation is closely linked to climate change over a range of timescales regardless of the mean climate state. More generally, the results further demonstrate the potential of benthic Mg/Ca ratios as a tool for reconstructing past ocean and climate conditions.
Open Access
Climate variability from Florida Bay sedimentary record: possible teleconnections to ENSO, PNA, and CNP
(Climate Research, 2002) Cronin, TM; Dwyer, GS; Schwede, SB; Dowsett, HJ
Open Access
Deep-sea ostracode species diversity: response to late Quaternary climate change
(Marine Micropaleontology, 1999) Cronin, TM; DeMartino, DM; Dwyer, GS; Rodriguez Lazaro, J
Open Access
Ecology and shell chemistry of Loxoconcha matagordensis
(PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 2005-09) Cronin, TM; Kamiya, T; Dwyer, GS; Belkin, H; Vann, CD; Schwede, S; Wagner, R
Open Access
Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay
(GLOBAL AND PLANETARY CHANGE, 2003-03) Cronin, TM; Dwyer, GS; Kamiya, T; Schwede, S; Willard, DA
Open Access
Mid-pliocene deep-sea bottom-water temperatures based on ostracode Mg/Ca ratios
(MARINE MICROPALEONTOLOGY, 2005-03) Cronin, TM; Dowsett, HJ; Dwyer, GS; Baker, PA; Chandler, MA
Open Access
Middle Pliocene sea surface temperature variability
(PALEOCEANOGRAPHY, 2005-06) Dowsett, HJ; Chandler, MA; Cronin, TM; Dwyer, GS
Open Access
Multiproxy evidence of Holocene climate variability from estuarine sediments, eastern North America
(PALEOCEANOGRAPHY, 2005-10) Cronin, TM; Thunell, R; Dwyer, GS; Saenger, C; Mann, ME; Vann, C; Seal, RR
Open Access
North atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles
(Science, 1995-12-01) Dwyer, GS; Cronin, TM; Baker, PA; Raymo, ME; Buzas, JS; Corrège, T
Variations in the ratio of magnesium to calcium (Mg/Ca) in fossil ostracodes from Deep Sea Drilling Project Site 607 in the deep North Atlantic show that the change in bottom water temperature during late Pliocene 41,000-year obliquity cycles averaged 1.5°C between 3.2 and 2.8 million years ago (Ma) and increased to 2.3°C between 2.8 and 2.3 Ma, coincidentally with the intensification of Northern Hemisphere glaciation. During the last two 100,000-year glacial-to-interglacial climatic cycles of the Quaternary, bottom water temperatures changed by 4.5°C. These results show that glacial deepwater cooling has intensified since 3.2 Ma, most likely as the result of progressively diminished deep-water production in the North Atlantic and of the greater influence of Antarctic bottom water in the North Atlantic during glacial periods. The ostracode Mg/Ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from Site 607, as well as derivation of a hypothetical sea-level curve for the late Pliocene and late Quaternary. The effects of dissolution on the Mg/Ca ratios of ostracode shells appear to have been minimal.
Open Access
Orbital and suborbital variability in North Atlantic bottom water temperature obtained from deep-sea ostracod Mg/Ca ratios
(PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 2000-09-15) Cronin, TM; Dwyer, GS; Baker, PA; Rodriguez-Lazaro, J; DeMartino, DM
Open Access
Population ecology and shell chemistry of a phytal ostracode species (Loxoconcha matagordensis) in the Chesapeake Bay watershed
(MARINE MICROPALEONTOLOGY, 2004-11) Vann, CD; Cronin, TM; Dwyer, GS