Abstract
ABSTRACTFinding direct evidence for atmospheric circulation change in terrestrial records of Holocene climate variability remains a fundamental challenge. Here we present the first combined stable oxygen and hydrogen isotopic palaeorecord from a peatland core in Newfoundland, Canada. Sphagnum cellulose samples were isolated from a core from Nordan's Pond Bog, Newfoundland, and analysed for δD values. Combined with existing δ18O data, the resulting δD/δ18O bi‐plot correlates directly with existing measurements of the modern (late 20th century) isotopic composition of precipitation from GNIP stations in Nova Scotia and Labrador, implying a close relationship between the estimated isotopic composition of source water used by the mosses and that of the source precipitation. We use the relative variations between the two isotope records to test the hypothesis that atmospheric circulation changed in the millennium following the 8.2‐ka BP climate event. The data reveal a secondary complex isotopic response ∼200 years (8250–8050 a BP) after a primary oxygen isotopic event that is widespread in the north Atlantic region. This secondary event is characterized by a divergence in oxygen and hydrogen isotope records that can most plausibly be explained by the augmentation of precipitation moisture from a more distant and more continental vapour source.
Highlights
Ensemble model-simulated projections for 21st-century climate in the North Atlantic region suggest future warming may be mitigated in part by a decrease in the heat transfer from low to higher latitudes associated with slow down in Atlantic Meridional Overturning Circulation (AMOC) (Hofmann and Rahmstorf, 2009; Collins et al, 2013)
Sample resolution was increased to one sample every 4 cm from $8400 to 8000 a BP and contiguous 1-cm samples were analysed across the primary isotopic event observed in the oxygen isotope stratigraphy, providing subcentennial and decadal resolution, respectively, such that hydrogen sample resolution equalled that of the oxygen record through 576–708 cm (7594–8812 a BP)
With the exception of the early Holocene event, dDSphagnum values show variation centred on $À120 Æ 10‰ with no general increasing or decreasing trend. dDSphagnum values through the early Holocene event exceeded the range of variability found throughout the rest of the record, albeit with a lower sampling resolution from $7950 (Æ 50) a BP to present
Summary
Ensemble model-simulated projections for 21st-century climate in the North Atlantic region suggest future warming may be mitigated in part by a decrease in the heat transfer from low to higher latitudes associated with slow down in Atlantic Meridional Overturning Circulation (AMOC) (Hofmann and Rahmstorf, 2009; Collins et al, 2013). Changes in the surface oceanic heat gradient between low and high latitudes will impact upon the gradient in atmospheric temperature, thereby influencing the strength and position of the northern mid-latitude atmospheric jetstream circulation (hereafter jet) (Tang et al, 2014; Francis and Vavrus, 2015). In this context, quantification of the impact of past changes in the northern mid-latitude atmospheric jet in response to oceanic circulation changes is valuable for constraining model simulations of similar scenarios in future climate projections (LeGrande and Schmidt, 2009; Tindall and Valdes, 2011; Holmes et al, 2016).
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