Sedimentary Proxy Evidence of a Mid-Holocene Hypsithermal Event in the Location of a Current Warming Hole, North Carolina, USA

Abstract

A wetland deposit from the southern Appalachian mountains of North Carolina, USA, has been radiocarbon dated and shows continuous deposition from the early Holocene to the present. Non-coastal records of Holocene paleoenvironments are rare from the southeastern USA. Increased stable carbon isotope ratios (?13C) of sedimentary organic matter and pollen percentages indicate warm, dry early- to mid-Holocene conditions. This interpretation is also supported by n-alkane biomarker data and bulk sedimentary C/N ratios. These warm, dry conditions coincide with a mid-Holocene hypsithermal, or altithermal, documented elsewhere in North America. Our data indicate that the southeastern USA warmed concurrently with much of the rest of the continent during the mid-Holocene. If the current "warming hole" in the southeastern USA persists, during a time of greenhouse gas-induced warming elsewhere, it will be anomalous both in space and time.

Changes in Holocene meridional circulation and poleward Atlantic flow: the Bay of Biscay as a nodal point

“…Small amplitude differences are observed between the two studied records, but synchronous warm periods are clearly identified between 8.2 and 7.4 and between 6.6 and 5.6 kyr BP, these intervals roughly corresponding to the upper and lower limits of the mid-Holocene hypsithermal in the North Atlantic region (e.g. Eynaud et al, 2004;Walker et al, 2012;Tanner et al, 2015).…”

Micromorphology of late Pleistocene and Holocene sediments and a new interpretation of the Holocene chronology at Anderson Pond, Tennessee, USA

“…No micromorphological or microfossil analyses were available for the site, but based on pedogenic characteristics of the paleosol and the lack of evidence of pedogenesis in the underlying sediments, the authors interpreted the mid-Holocene paleosol to indicate a period of warming and drying climate associated with the hypsithermal. A recent study by Tanner et al (2015) of a bog in southwestern North Carolina also presented sedimentary proxy evidence of a mid-Holocene “hypsithermal event” characterized by less negative δ 13 C values of SOM and by organic biomarker n-alkane distributions that show an increase of the C 18 chain length during the middle Holocene; C 18 is a biomarker for bacteria and suggests organic matter breakdown, which would be expected in a warm, dry climate with extensive organic matter oxidation. Comparison with Holocene records from the US Great Plains (Nordt et al, 2008) and the middle Atlantic region of the United States (Stinchcomb et al, 2013) indicates that the stable carbon isotope expression of the middle Holocene thermal maximum shows evidence for at least two, and possibly as many as four, major episodes of drought in the Great Plains and middle Atlantic regions, manifested by excursions of 2–5 per mil toward less negative δ 13 C values.…”

A Macroscopic Charcoal and Multiproxy Record from Peat Recovered from Depression Marshes in Longleaf Pine Sandhills, Florida, USA

“…As summarized in Tanner et al [31], high C/N ratios (generally above 20) are associated with vascular land plant organic matter, whereas lower C/N ratios suggest increased algal contributions (algal C/N generally between 4 and 10) and wetter conditions [32], although C/N ratios cannot always be confidently tied to vegetation changes in all environments [33]. Carbon isotope ratios of organic matter can be used as a climate proxy because the proportion of plants using the C3 (δ 13 C ≈ −28 ) vs. C4 (δ 13 C ≈ −14 ) photosynthetic pathway in a given setting is controlled largely by the temperature, aridity, exposure to sunlight, and atmospheric pCO 2 .…”

“…Therefore, significant drying of our field sites should result in the presence of increased C4 species, and a resulting increase in the δ 13 C values. These proxies have been successfully used to infer dry periods recorded in other southeastern USA wetlands [31].…”