Northeastern Patagonian Glacier Advances (43°S) Reflect Northward Migration of the Southern Westerlies Towards the End of the Last Glaciation

The last glacial termination was a key event during Earth’s Quaternary history that was associated with rapid, high-magnitude environmental and climatic change. Identifying its trigger mechanisms is critical for understanding Earth’s modern climate system over millennial timescales. It has been proposed that latitudinal shifts of the Southern Hemisphere Westerly Wind belt and the coupled Subtropical Front are important components of the changes leading to global deglaciation, making them essential to investigate and reconstruct empirically. The Patagonian Andes are part of the only continental landmass that fully intersects the Southern Westerly Winds, and thus present an opportunity to study their former latitudinal migrations through time and to constrain southern mid-latitude palaeo-climates. Here we use a combination of geomorphological mapping, terrestrial cosmogenic nuclide exposure dating and glacial numerical modelling to reconstruct the late-Last Glacial Maximum (LGM) behaviour and surface mass balance of two mountain glaciers of northeastern Patagonia (43°S, 71°W), the El Loro and Río Comisario palaeo-glaciers. In both valleys, we find geomorphological evidence of glacier advances that occurred after the retreat of the main ice-sheet outlet glacier from its LGM margins. We date the outermost moraine in the El Loro valley to 18.0 ± 1.15 ka. Moreover, a series of moraine-matching simulations were run for both glaciers using a spatially-distributed ice-flow model coupled with a positive degree-day surface mass balance parameterisation. Following a correction for cumulative local surface uplift resulting from glacial isostatic adjustment since ∼18 ka, which we estimate to be ∼130 m, the glacier model suggests that regional mean annual temperatures were between 1.9 and 2.8°C lower than present at around 18.0 ± 1.15 ka, while precipitation was between ∼50 and ∼380% higher than today. Our findings support the proposed equatorward migration of the precipitation-bearing Southern Westerly Wind belt towards the end of the LGM, between ∼19.5 and ∼18 ka, which caused more humid conditions towards the eastern margins of the northern Patagonian Ice Sheet a few centuries ahead of widespread deglaciation across the cordillera.

An Investigation into New Zealand's Climate During the Last Glacial Maximum: a Climate Modelling Approach

<p>New Zealand's climate during the Last Glacial Maximum has been investigated using the UKMO global and regional models HadAM3H (GCM) and HadRM3H (RCM). SSTs and sea-ice were supplied from a set of prior coupled model (HadCM3) runs and all models were set up according to the glacial conditions as specified by PMIP. In the analysis of the global simulation, emphasis was placed on the climate of the Southern Hemisphere. Compared to the present day, the modelled climate of the LGM is mainly characterized by the different wind regimes, both in the zonal and meridional directions. In the zonal mean, the polar trough shifted equatorward, and the westerly wind increased slightly between approximately 30 degrees S-50 degrees S, and decreased poleward of this zonal band. At the same time, there was an increase in the number of and/or strength of southerlies between 35 degrees S-60 degrees S. This resulted in a reduction of the poleward zonal mean meridional heat transport, and an enhancement of the wave number 3 pattern in the mean zonal circulation. All these changes contributed to a weaker SAO during the LGM. Interannual variability was as today, dominated by the High Latitude Mode (HLM, or Antarctic Oscillation/Southern Annular Mode) and ENSO. For the LGM, New Zealand was about 2.5 degrees C-4 degrees C cooler than in a pre-industrial control simulation. The seasonal cooling was largest during winter. Excluding the Alpine region, the largest cooling geographically took place in the east of the South Island. Precipitation was in general reduced everywhere during the whole year, except for the east of the South Island. The westerly wind increased considerably over the North Island and the northern part of the South Island, but was weaker over the rest of the South Island. JJA was the exception with weaker westerly winds over all New Zealand which was probably related to enhance blocking during that season. The stronger westerly wind accentuated the cooling over the North Island, except for the eastern region, where it mainly enhanced the dry conditions by preventing the moist easterly winds coming ashore. The weaker westerly wind in the south on the other hand encouraged enhanced penetration of moist winds. The most dramatic change in the modelled New Zealand climate was the large increase in the number of southerlies in each region, which were capable of bringing very cold polar air over most of the country. It was probably mainly the changes in the winds that lead to the harshness of New Zealand's climate during the LGM, increasing the seasonality in temperature and precipitation. It is suggested that they had therefore a controlling influence on the existence of some of the vegetation types in New Zealand.</p>

An Investigation into New Zealand's Climate During the Last Glacial Maximum: a Climate Modelling Approach

<p>New Zealand's climate during the Last Glacial Maximum has been investigated using the UKMO global and regional models HadAM3H (GCM) and HadRM3H (RCM). SSTs and sea-ice were supplied from a set of prior coupled model (HadCM3) runs and all models were set up according to the glacial conditions as specified by PMIP. In the analysis of the global simulation, emphasis was placed on the climate of the Southern Hemisphere. Compared to the present day, the modelled climate of the LGM is mainly characterized by the different wind regimes, both in the zonal and meridional directions. In the zonal mean, the polar trough shifted equatorward, and the westerly wind increased slightly between approximately 30 degrees S-50 degrees S, and decreased poleward of this zonal band. At the same time, there was an increase in the number of and/or strength of southerlies between 35 degrees S-60 degrees S. This resulted in a reduction of the poleward zonal mean meridional heat transport, and an enhancement of the wave number 3 pattern in the mean zonal circulation. All these changes contributed to a weaker SAO during the LGM. Interannual variability was as today, dominated by the High Latitude Mode (HLM, or Antarctic Oscillation/Southern Annular Mode) and ENSO. For the LGM, New Zealand was about 2.5 degrees C-4 degrees C cooler than in a pre-industrial control simulation. The seasonal cooling was largest during winter. Excluding the Alpine region, the largest cooling geographically took place in the east of the South Island. Precipitation was in general reduced everywhere during the whole year, except for the east of the South Island. The westerly wind increased considerably over the North Island and the northern part of the South Island, but was weaker over the rest of the South Island. JJA was the exception with weaker westerly winds over all New Zealand which was probably related to enhance blocking during that season. The stronger westerly wind accentuated the cooling over the North Island, except for the eastern region, where it mainly enhanced the dry conditions by preventing the moist easterly winds coming ashore. The weaker westerly wind in the south on the other hand encouraged enhanced penetration of moist winds. The most dramatic change in the modelled New Zealand climate was the large increase in the number of southerlies in each region, which were capable of bringing very cold polar air over most of the country. It was probably mainly the changes in the winds that lead to the harshness of New Zealand's climate during the LGM, increasing the seasonality in temperature and precipitation. It is suggested that they had therefore a controlling influence on the existence of some of the vegetation types in New Zealand.</p>

Possible linkage between asymmetry of atmospheric meridional circulation and tropical cyclones in the Central Pacific during El Niño years

The El Niño–Southern Oscillation is one of the most important drivers of climate change on Earth, and is characterised by warmer (El Niño) or colder (La Niña) ocean surface temperatures in the equatorial Pacific. Tropical cyclones (TCs) and meridional circulation are the most influential weather events and climate phenomena, respectively. However, the link between TCs and meridional circulation anomalies (MCA) during El Niño years is unclear. Therefore, we calculated the accumulated cyclone energy index of TCs and the mass stream function of MCA from 1980 to 2018. Our results showed that TCs were closely related to the asymmetry of the MCA in the Central Pacific during El Niño years. An updraft anomaly in the North Pacific was found, which affected the response of MCA to El Niño from May to October during El Niño years. Therefore, the MCA intensity difference between the North and South Pacific increased, and the asymmetry was strengthened. This phenomenon may be strengthened by the combined effects of the equatorial westerly wind, relative vorticity, and warm ocean surfaces, which are controlled by El Niño. The equatorial westerly wind produces positive shear north of the equator, which increases the relative vorticity. The increase in relative vorticity is accompanied by a monsoon trough, leading to increased precipitation and updrafts. The background of the relative vorticity, updraft, and monsoon trough may be conducive to the generation and development of TCs. Our results prove that the possible link between TCs and the asymmetry of the MCA during El Niño years is derived from the combined effect of the equatorial westerly wind, relative vorticity, and warm ocean surfaces, thus providing a partial explanation for the link between TCs and the MCA.

Early Holocene permafrost retreat in West Siberia amplified by reorganization of westerly wind systems

Rapid permafrost degradation and peatland expansion occurred in Eurasia during the Early Holocene and may be analogous to the region’s response to anthropogenic warming. Here we present a 230Th-dated, multiproxy speleothem record with subdecadal sampling resolution from Kyok-Tash Cave, at the modern permafrost margin in the northern Altai Mountains, southwestern Siberia. Stalagmite K4, covering the period 11,400 to 8,900 years before present, indicates an absence of stable permafrost within three centuries of the Younger Dryas termination. Between 11,400 and 10,400 years ago, speleothem δ18O is antiphased between the Altai and Ural ranges, suggesting a reorganization of the westerly wind systems that led to warmer and wetter winters over West Siberia and Altai, relative to the zonally adjacent regions of Northern Eurasia. At the same time, there is evidence of peak permafrost degradation and peatland expansion in West Siberia, consistent with the interpreted climate anomaly. Based on these findings, we suggest that modern permafrost in Eurasia is sensitive to feedbacks in the ocean-cryosphere system, which are projected to alter circulation regimes over the continent.

Research of sources and distribution of suspended matter in Omega Bay (Crimea) based on expeditional data and numerical simulation

The regularities of the suspended matter distribution in the system of wind currents from the area of bottom elevation along the Omega Bay are revealed. Observational data show that in the region of bottom elevation there is a topographic quasi-stationary eddy cell accumulating pollutants. Based on numerical modeling, it is revealed that the meridional winds of all directions contribute to the transfer of the suspended matter from the area of elevation to the western coast of the bay to the beach area, to a small coastal area with a characteristic bend of the coastline. The most significant suspended matter flows are generated by northeasterly and southeasterly winds. With a westerly wind, the main flow of suspended matter is directed to the eastern coast of the bay. The weak easterly winds, typical for Sevastopol, do not cause the removal of suspended matter from the central area of the investigated bay.

The essential role of early-spring westerly wind burst in generating the centennial extreme 1997/98 El Niño

While both intrinsic low-frequency atmosphere–ocean interaction and multiplicative burst-like event affect the development of the El Niño–Southern Oscillation (ENSO), the strong nonlinearity in ENSO dynamics has prevented us from separating their relative contributions. Here we propose an online filtering scheme to estimate the role of the westerly wind bursts (WWBs), a type of aperiodic burst-like atmospheric perturbation over the western-central tropical Pacific, in the genesis of the centennial extreme 1997/98 El Niño using the CESM coupled model. This scheme highlights the deterministic part of ENSO dynamics during model integration, and clearly demonstrates that the strong and long-lasting WWB in March 1997 was essential for generating the 1997/98 El Niño. Without this WWB, the intrinsic low-frequency coupling would have only produced a weak warm event in late 1997 similar to the 2014/15 El Niño.

Regional validation of the use of diatoms in ice cores from the Antarctic Peninsula as a Southern Hemisphere Westerly Wind proxy

The Southern Hemisphere Westerly Winds are among the most important drivers of recently observed environmental changes in West Antarctica. However, the lack of long-term wind records in this region hinders our ability to assess the long-term context of these variations. Ice core proxy records yield valuable information about past environmental changes, although current proxies present limitations when aiming to reconstruct past winds. Here we present the first regional wind study based on the novel use of diatoms preserved in Antarctic ice cores. We assess the temporal variability in diatom abundance and its relation to regional environmental parameters spanning a 20-year period across three sites in the southern Antarctic Peninsula and Ellsworth Land, Antarctica. Correlation analyses reveal that the temporal variability of diatom abundance from high elevation ice core sites is driven by changes in wind strength over the core of the Southern Hemisphere Westerly Wind belt. Validating the use of diatoms preserved in ice cores from the Southern Antarctic Peninsula and Ellsworth Land as a proxy for reconstructing past variations in wind strength over the Pacific sector of the Southern Hemisphere Westerly Wind belt.