Late-Holocene climate and ecosystem history from Chesapeake Bay sediment cores, USA

Abstract

Abstract:Palaeoclimate records from late-Holocene sediments in Chesapeake Bay, the largest estuary in the USA, provide evidence that both decadal to centennial climate variability and European colonization had severe impacts on the watershed and estuary. Using pollen and dino agellate cysts as proxies for mid-Atlantic regional precipitation, estuarine salinity and dissolved oxygen (DO) during the last 2300 years, we identi ed four dry intervals, centred on ad 50 (P1/D1), ad 1000 (P2/D2), ad 1400 (P3) and ad 1600 (P4). Two centennial-scale events, P1/D1 and P2/D2, altered forest composition and led to increased salinity and DO levels in the estuary. Intervals P3 and P4 lasted several decades, leading to decreased production of pine pollen. Periods of dry midAtlantic climate correspond to 'megadroughts' identi ed from tree-ring records in the southeastern and central USA. The observed mid-Atlantic climate variability may be explained by changes in atmospheric circulation resulting in longer-term, perhaps ampli ed, intervals of meridional ow. After European colonization in the early seventeenth century, forest clearance for agriculture, timber and urbanization altered estuarine water quality, with dino agellate assemblages indicating reduced DO and increased turbidity.

Historical records of coastal eutrophication-induced hypoxia

“…In area column B = Baltic; D = Denmark; F = Finland; N = Norway; S = Spain; Fla = Florida; Mx = Mexico. See Brush (2001), Cronin and Vann (2003), Kemp et al (2000) and Rabalais et al (2007) Andrén et al (1999); 7) Barmawidjaja et al (1995); 8) Blackwelder et al (1996); 9) Bratton et al (2003) ; 10) Brunner (2006); 11) Cearreta et al (2000); 12) Chen et al (2001); 13) Chmura et al (2004); 14) Clarke et al (2003); 15) Clarke et al (2006); 16) Colman and Bratton (2003); 17) Cooper (1995); 18) Brush (1991, 1993); 19) Cornwell et al (1996); 20) Cronin and Vann (2003) Thomas et al (2000Thomas et al ( , 2004; 55) Toyoda and Kitazato (1995); 56) Tsujimoto et al (2006a); 57) Tsujimoto et al (2008); 58) Turner and Rabalais (1994); 59) Turner et al (2004); 60) Turner et al (2006); 61) Voss and Struck (1997); 62) Willard et al (2003); 63) Yasuhara et al (2003); 64) Yasuhara and Yamazaki (2005); 65) Yasuhara et al (2007); 66) Zheng et al (2003); 67) Zimmerman and Canuel (2000); 68) Zimmerman and Canuel (2001); 69) Zimmerman and Canuel (2002) …”

“…Large standing stocks of a few hypoxia-tolerant species may reflect the disappearance of macrofaunal and meiofaunal predators combined with an abundant food supply. On the Pakistan margin of the Arabian Sea, foraminiferans replace the metazoan macrofauna as the principal consumers of organic matter at oxygen concentrations below 5-7 µM (Woulds et al, 2007).…”

“…Willard et al (2003) estimated dissolved oxygen values in cores from Chesapeake Bay using a modern analogue technique based on dinocyst species (Fig. 13).…”

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

“…Thus, bay temperature variability should reflect that of its source water in the MAB, and more broadly, ocean-atmosphere Karlsen et al (2000), Cronin et al (2000), Zimmerman and Canuel (2002). 2 -Brush (1989), Willard et al (2003). processes originating in subpolar regions of the Northern Hemisphere.…”

“…Sediment at this site was deposited at a near constant rate of 0.36 cm yr − 1 during the last 2100 years and includes a 20th century sediment record. Sample ages for RD-2209 were estimated using the age model described fully in Willard et al (2003). A zone of slow sedimentation or intermittent non-deposition occurs at 800-900 cm core depth estimated to represent the interval about 2100-5000 calibrated years age (Colman et al, 2002).…”