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
Palynomorph, ostracode, and benthic foraminiferal assemblages from Lake Pontchartrain sediment cores were analyzed to reconstruct long-term trends in regional vegetation and salinity in the lake. Pollen assemblages from two short cores (9-7-96-7 and 9-7-96-9), mostly deposited after 1950 AD, indicate dominance ofPinus pollen and the common occurrence of Pediastrum, a colonial green alga typically indicative of eutrophication, throughout this time. A longer core (3.47 m), LP 97-la, includes middle Holocene sediments (5.5-4.2 ka), characterized by higher salinities and greater abundance of Quercus pollen. Younger sediments in this core record a transition to meso-to oligohaline conditions and wetter conditions later in the Holocene. The upper 30-40 cm of LP 97-la represents sediment deposition after 1950 AD. These sediments are characterized by oligohaline to limnic ostracode faunas and unprecedented abundance of colonial green algae indicative of eutrophication. This may represent the response of phytoplankton and benthic communities to the introduction of Mississippi River water and sediment resuspension resulting from openings of the Bonnet Carre' spillway during the last half of the 20th century.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.