An official website of the United States government
Changes in ice-sheet size impact atmospheric circulation, a phenomenon documented by models but constrained by few paleoclimate records. We present sub-centennial-scale records of summer temperature and summer precipitation hydrogen isotope ratios (δ2H) spanning 12–7 kiloannum (ka) from a lake on Baffin Island. In a transient model simulation, winds in this region were controlled by the relative strength of the high-pressure systems and associated anticyclonic circulation over the retreating Greenland and Laurentide ice sheets. The correlation between summer temperature and precipitation δ2H proxy records changed from negative to positive at 9.8 ka. This correlation structure indicates a shift from alternating local and remote moisture, governed by the two ice-sheet high-pressure systems, to only remote moisture after 9.8 ka, governed by the strong Greenland high-pressure system after the Laurentide Ice Sheet retreated. Such rapid atmospheric circulation changes may also occur in response to future, gradual ice-sheet retreat.
more »
« less
Near-surface winds at the southern Laurentide ice margin through the last deglaciation
Terrestrial proxies of wind direction spanning the last deglaciation suggest easterly winds were present near the Laurentide Ice Sheet margin in the North American midcontinent. However, the existence and spatial extent of such easterly winds have not been investigated with transient paleoclimate model simulations, which could provide improved dynamical context for interpreting the causes of these winds. Here we assess near-surface winds near the retreating southern Laurentide Ice Sheet margin using iTRACE, a transient simulation of deglacial climate from 20–11 ka. Near the south-central margin, simulated near-surface winds are northeasterly to easterly through the deglaciation, due to katabatic flow off the ice sheet and anticyclonic circulation. As the ice sheet retreats and the Laurentide High moves northeastward and weakens, near-surface northeasterly winds weaken. Meltwater fluxes also influence temperature and sea level pressure over the North Atlantic, leading to easterly wind anomalies over eastern to midwestern North America. The agreement between proxy and model wind directions is promising, although simulated easterly to northeasterly winds extend too far south in iTRACE relative to the proxy data. Agreement is also strongest in winter, spring, and fall, suggesting these may have been seasons with greater aeolian activity.
more »
« less
- PAR ID:
- 10613525
- Publisher / Repository:
- Quaternary Research
- Date Published:
- Journal Name:
- Quaternary Research
- Volume:
- 125
- ISSN:
- 0033-5894
- Page Range / eLocation ID:
- 87 to 103
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
During the last deglaciation, collapse of the saddle between the North American Cordilleran and Laurentide ice sheets led to rapid ice-sheet mass loss and separation, with meltwater discharge contributing to deglacial sea level rise. We directly date ice-sheet separation at the end of the saddle collapse using 64 10Be exposure ages along an ~1200-km transect of the ice-sheet suture zone. Collapse began in the south by 15.4 ± 0.4 ka and ended by 13.8 ± 0.1 ka at ~56◦N. Ice-sheet model simulations consistent with the 10Be ages find that the saddle collapse contributed 6.2–7.2 m to global mean sea-level rise from ~15.5 ka to ~14.0 ka, or approximately one third of global mean sea-level rise over this period. We determine 3.1–3.6 m of the saddle collapse meltwater was released during Meltwater Pulse 1A ~14.6-14.3 ka, constituting 20–40% of this meltwater pulse’s volume. Because the separation of the Cordilleran and Laurentide ice sheets occurred over 1–2 millennia, the associated release of meltwater during the saddle collapse supplied a smaller contribution to the magnitude of Meltwater Pulse 1A than has been recently proposed.more » « less
-
Accurate reconstruction of Laurentide Ice Sheet volume changes following the Last Glacial Maximum is critical for understanding ice sheet contribution to sea-level rise, the resulting influence of meltwater on oceanic circulation, and the spatial and temporal patterns of deglaciation. Here, we provide empirical constraints on Laurentide Ice Sheet thinning during the last deglaciation by measuring in situ cosmogenic 10Be in 81 samples collected along vertical transects of nine mountains in the northeastern United States. In conjunction with 107 exposure age samples over five vertical transects from previous studies, we reconstruct ice sheet thinning history. At peripheral sites (within 200 km of the terminal moraine), we find evidence for ∼600 m of thinning between 19.5 ka and 17.5 ka, which is coincident with the slow initial margin retreat indicated by varve records. At locations >400 km north of the terminal moraine, exposure ages above and below 1200 m a.s.l. exhibit different patterns. Ages above this elevation are variable and older, while lower elevation ages are indistinguishable over 800−1000 m elevation ranges, a pattern that suggests a subglacial thermal boundary at ∼1200 m a.s.l. separating erosive, warm-based ice below and polythermal, minimally erosive ice above. Low-elevation ages from up-ice mountains are between 15 ka and 13 ka, which suggests rapid thinning of ∼1000 m coincident with Bølling-Allerød warming. These rates of rapid paleo-ice thinning are comparable to those of other vertical exposure age transects around the world and may have been faster than modern basin-wide thinning rates in Antarctica and Greenland, which suggests that the southeastern Laurentide Ice Sheet was highly sensitive to a warming climate.more » « less
-
Abstract This study examines the climate response to a sea surface temperature (SST) warming imposed over the southwest Tropical Indian Ocean (TIO) in a coupled ocean-atmosphere model. The results indicate that the southwest TIO SST warming can remotely modulate the atmospheric circulation over the western North Pacific (WNP) via inter-basin air-sea interaction during early boreal summer. The southwest TIO SST warming induces a “C-shaped” wind response with northeasterly and northwesterly anomalies over the north and south TIO, respectively. The northeasterly wind anomalies contribute to the north TIO SST warming via a positive Wind-Evaporation-SST(WES) feedback after the Asian summer monsoon onset. In June, the easterly wind response extends into the WNP, inducing an SST cooling by WES feedback on the background trade winds. Both the north TIO SST warming and the WNP SST cooling contribute to an anomalous anticyclonic circulation (AAC) over the WNP. The north TIO SST warming, WNP SST cooling, and AAC constitute an inter-basin coupled mode called the Indo-western Pacific ocean capacitor (IPOC), and the southwest TIO SST warming could be a trigger for IPOC. While the summertime southwest TIO SST warming is often associated with antecedent El Niño, the warming in 2020 seems to be related to extreme Indian Ocean Dipole in 2019 fall. The strong southwest TIO SST warming seems to partly explain the strong summer AAC of 2020 over the WNP even without a strong antecedent El Niño.more » « less
-
We test the hypothesis that glacier systems, located in continental regions proximal to the Laurentide Ice Sheet (LIS), had local ice maxima considerably earlier than the LIS maximum and thus before the insolation minima at ~21 ka. Ranges located in the northwest US exhibit earlier deglaciation timing between ~23 and 22 ka, except for the Yellowstone region where younger time-transgressive ages complicate regional interpretations and the northern Montana ice cap where late glacial ages have recently been produced. Constraining the glacial history of more ice sheet-proximal alpine glaciers provides insight into whether the contrasting maximum-ice times in the northern Rocky Mountains were caused by regional climatic differences, such as anticyclonic wind patterns driven by the presence of the LIS. In the Pioneer Mountains of Montana, we measured in situ cosmogenic 10Be in 35 boulders on moraines marking the maximum Late Pleistocene positions of alpine glaciers from three valleys. The 10Be samples produced a range of ages, spanning pre Bull Lake to the last glaciation (i.e., Pinedale/Marine Isotope Stage (MIS) 2). We find an average exposure age for initial deglaciation of 18.2 ±0.9 during the local Last Glacial Maximum, indicative of synchronous retreat in the Pioneer Mountains. The similarity of initial deglaciation timing of the Pioneer Mountain glaciers with the northwestern Yellowstone glacial system and northern MT ice cap suggests that topography more proximal to the LIS margin maintained full ice extent longer. Our findings, in context of previous work, suggest that in the case of the Pioneer Mountains their more proximal location to the ice margin may have delayed onset of deglaciation by greater exposure to local cooling from katabatic winds and/or additional moisture sourced from large ice-marginal glacial lakes, hence the lack of earlier deglacial ages like those found further to the west and east of the northern Rocky Mountain cordillera.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1017/qua.2024.62
