Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay

Abstract

We present paleoclimate evidence for rapid ( < 100 years) shifts of f 2-4 jC in Chesapeake Bay (CB) temperature f2100, 1600, 950, 650, 400 and 150 years before present (years BP) reconstructed from magnesium/calcium (Mg/Ca) paleothermometry. These include large temperature excursions during the Little Ice Age (f1400 -1900 AD) and the Medieval Warm Period (f800 -1300 AD) possibly related to changes in the strength of North Atlantic thermohaline circulation (THC). Evidence is presented for a long period of sustained regional and North Atlantic-wide warmth with low-amplitude temperature variability between f450 and 1000 AD. In addition to centennial-scale temperature shifts, the existence of numerous temperature maxima between 2200 and 250 years BP (average f70 years) suggests that multi-decadal processes typical of the North Atlantic Oscillation (NAO) are an inherent feature of late Holocene climate. However, late 19th and 20th century temperature extremes in Chesapeake Bay associated with NAO climate variability exceeded those of the prior 2000 years, including the interval 450 -1000 AD, by 2 -3 jC, suggesting anomalous recent behavior of the climate system. D

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

“…A total of 258 samples from MD03-2661 yielded L. matagordensis suitable for analysis (see chronology); the RD-2209 record included 450 analyses . Mg/Ca ratios were converted to warm-season temperature using the calibration equation y =0.644x −2.4284 (r 2 =0.805) derived from field, culturing and laboratory analyses of Loxoconcha from Chesapeake Bay and the adjacent continental shelf (Dwyer et al, 2002;Cronin et al, 2003;Vann et al, 2004). These calibration studies demonstrated that temperature is the primary factor influencing Chesapeake Bay Loxoconcha Mg/Ca ratios and, at least over the sampled salinity range (~15-35 psu), salinity does not appear to be important.…”

“…1 inset). These include a 17.2-m long core MD99-2209 (38°53.18′N and 76°23.68′W, water depth 25 m), nearby core RD-98 (Colman et al, 2002) and core PTXT-2 from off the Patuxent River (38°19.58′N and 76°23.55′W, water depth 11.5 m) that produced the paleotemperature record discussed in Cronin et al (2003). This composite curve, referred to as RD-2209, covers the last 2200 years and has been incorporated into several northern hemisphere surface temperature reconstructions covering the last 2000 years (e.g.…”

On past temperatures and anomalous late‐20th‐century warmth

“…All series are shown with respect to the 1961-90 base period. [Mann et al, 1999]; "Chesapeake Bay" [Cronin et al, 2003]; "W. Greenland" [Fisher et al, 1996]; "Tornetrask" [Grudd et al, 2002]; "Low Countries" [van Engelen et al, 2001); "Yamal" [Hantemirov andShiyatov, 2002, reprocessed in Briffa, 2000]; "Taimyr" [Naurzbaev et al, 2002]; "Mongolia" [D'Arrigo et al, 2001]; "China" [Yang et al, 2002].…”

Population ecology and shell chemistry of a phytal ostracode species (Loxoconcha matagordensis) in the Chesapeake Bay watershed

“…Semi-transparent-opaque shells that wintered-over from the previous season are less correlated with water temperature than newly secreted transparent shells at Dameron Marsh, Site 2. notable periods of low Mg/Ca and Sr/Ca ratios in core PTXT-2-P-5 (~1530-1550, 1680, 1780-1810, 1840 AD) and core RD-K-98 (~1750, 1790, 1840-1850 (Fig. 12b), which seem to signify cool regional conditions during parts of the Little Ice Age (Cronin et al, 2003).…”

“…Loxoconcha matagordensis specimens were isolated and picked from Z. marina samples following Cronin et al, 2003 for core data and chronology). Cores RD-K-98 (~400 cm) and MD99-2209 (1720 cm) were from the same location and the uppermost 800 cm of MD99-2209 were spliced together with the RD-K-98 record to provide the longest record of fossil Loxoconcha shells that dated back to~2200 years before present.…”