Weak precipitation δ2H response to large Holocene hydroclimate changes in eastern North America. (15th March 2023)

• Record Type: Journal Article
• Authors: Stefanescu, Ioana C.; Shuman, Bryan N.; Grigg, Laurie D.; Bailey, Adriana; Stefanova, Vania; Oswald, W. Wyatt
• Is Part Of: Quaternary science reviews. Volume 304(2023)
• Publication Date: 2023-03-15
• Subjects: Leaf wax records -- Holocene climate -- Eastern north america -- Precipitation isotopes; Geology, Stratigraphic -- Quaternary -- Periodicals; Stratigraphie -- Quaternaire -- Périodiques; 551.79
• DOI: 10.1016/j.quascirev.2023.107990
• Languages: English
• ISSNs: 0277-3791

Abstract

Abstract: In eastern North America, annual precipitation increased by >40% over the Holocene, largely in response to melting of the Laurentide Ice Sheet. The change substantially raised lake levels and transformed conifer-dominated ecosystems into mesic deciduous forests. δ 2 H values of terrestrially derived leaf-wax n -alkanes can facilitate diagnoses of the climate dynamics involved by reconstructing δ 2 H values of mean annual precipitation (δ 2 HMAP ). However, competing influences on δ 2 HMAP values in the mid-latitudes, such as changes in moisture sources and in the seasonal distribution of precipitation, can generate confounding effects. To test δ 2 HMAP sensitivity to potential changes associated with the final Holocene phases of deglaciation in eastern North America, we used 14 fossil-pollen records to reconstruct monthly precipitation changes and to model δ 2 HMAP values during the Holocene. The pollen-inferred precipitation increased by 100–200 mm during both cold and warm seasons, but modeled δ 2 HMAP values changed by only ∼10‰, because isotopically-heavy summer precipitation increased by nearly as much as the cold-season isotopically-light winter precipitation. Three new leaf wax n -C29 -alkane (δ 2 HC29 ) records spanning the Holocene from Vermont, Pennsylvania, and Massachusetts closely follow modeled δ 2 HMAP trends and confirm only a small decline in δ 2 HMAP values over the Holocene. Because the shifts in precipitation seasonality accurately predict the n -alkane records, changes in moisture sources or pathways appear to play only a minor role in the regional δ 2 HMAP history despite the effects of deglaciation on atmospheric circulation. Soil evaporation also did not significantly alter δ 2 HC29 values from the values predicted using the pollen-derived reconstructions. The results affirm that δ 2 HC29 values faithfully detected anticipated isotopic changes in δ 2 HMAP values, but that important paleoclimate events may not always yield strong changes in δ 2 HMAP values. Highlights: Leaf-wax records infer small precipitation δ 2 H changes during the Holocene. Fossil pollen indicates major increases in seasonal precipitation. Reconstructed δ 2 H values closely track those modeled from the fossil-pollen. Competing effects of seasonal precipitation limit δ 2 H changes in the mid-latitudes.