Multiproxy evidence of Holocene climate variability from estuarine sediments, eastern North America

Abstract

[1] We reconstructed paleoclimate patterns from oxygen and carbon isotope records from the fossil estuarine benthic foraminifera Elphidium and Mg/Ca ratios from the ostracode Loxoconcha from sediment cores from Chesapeake Bay to examine the Holocene evolution of North Atlantic Oscillation (NAO)-type climate variability. Precipitation-driven river discharge and regional temperature variability are the primary influences on Chesapeake Bay salinity and water temperature, respectively. We first calibrated modern d 18O water to salinity and applied this relationship to calculate trends in paleosalinity from the d 18 O foram , correcting for changes in water temperature estimated from ostracode Mg/Ca ratios. The results indicate a much drier early Holocene in which mean paleosalinity was $28 ppt in the northern bay, falling $25% to $20 ppt during the late Holocene. Early Holocene Mg/Ca-derived temperatures varied in a relatively narrow range of 13°to 16°C with a mean temperature of 14.2°C and excursions above 16°C; the late Holocene was on average cooler (mean temperature of 12.8°C). In addition to the large contrast between early and late Holocene regional climate conditions, multidecadal (20-40 years) salinity and temperature variability is an inherent part of the region's climate during both the early and late Holocene, including the Medieval Warm Period and Little Ice Age. These patterns are similar to those observed during the twentieth century caused by NAO-related processes. Comparison of the midlatitude Chesapeake Bay salinity record with tropical climate records of Intertropical Convergence Zone fluctuations inferred from the Cariaco Basin titanium record suggests an anticorrelation between precipitation in the two regions at both millennial and centennial timescales.

Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr

“…This modulation was further evidenced off Florida, at the inception of the Gulf Stream, by Lund et al (2006) who estimated a 10 % decrease in the flow of this current at the transition from the MCA to the LIA. Similarly, in the nearby Chesapeake Bay, such modulations were also evidenced by Cronin et al (2005) who linked this to North Atlantic Oscillation (NAO) forcing of sea surface temperature in the western North Atlantic.…”

The Medieval Climate Anomaly and Little Ice Age in Chesapeake Bay and the North Atlantic Ocean

“…Foraminiferal δ 18 O is generally controlled by water temperature and the oxygen isotope composition of seawater in which the foraminifera calcified. In CB, the δ 18 O baywater mainly reflects discharge-driven hydrological variability and the mixing of fresh and marine endmembers, which influences the δ 18 O of bay benthic foraminifera (δ 18 O foram ) (Cronin et al, 2005;Saenger et al, 2006). Five to ten specimens of the benthic foraminifera Elphidium selseyense were analyzed from each MD03-2661 sample for δ 18 O at the University of South Carolina stable isotope lab using a GV Isoprime stable isotope ratio mass spectrometer.…”

“…A total of 488 isotopic analyses were performed yielding a temporal resolution of about 5 years (see chronology). Paired downcore foraminiferal isotope and ostracode Mg/Ca measurements for 354 samples yielding both measurements were used to correct δ 18 O foram values for temperature and to estimate δ 18 O baywater following methods in Cronin et al (2005).…”

“…Rainfall and river discharge also influence the bay's oxygen isotopic composition (δ 18 O baywater ), as isotopically depleted freshwater water (~−7 to −9‰) mixes with enriched marine water (~0‰). To a first approximation, more rainfall leads to greater discharge, a stronger pycnocline, lower salinity, and depleted δ 18 O values; however bottom waters are more strongly influenced by more saline, denser marine water (Cronin et al, 2005).…”

Interpretation of benthic foraminiferal stable isotopes in subtidal estuarine environments

“…Paired measurements of bottom water δ 13 C DIC , δ 18 O w and salinity at Bono are used here to create a mixing model of sea and river water for the Auray estuary (e.g., Thomas et al, 2000;Polyak et al, 2003;Reinhart et al, 2003;Bauch et al, 2004;Cronin et al, 2005;McGann, 2008 strong linear relation with salinity ( Fig. 3).…”