Holocene sediment transport and climate variability of offshore Adélie Land, East Antarctica

<p>Grain size analysis of the terrigenous fraction of a laminated diatom ooze dating back to 11.4 kyr recovered offshore Adélie Land, East Antarctic margin was used to examine variations in sediment transport, depositional environments and Holocene climate variability at the location. Interpretations were assisted by additional proxies of primary productivity (δ¹³CFA, BSi%), glacial meltwater input (δDFA) and subsurface temperature (TEXL₈₆). Three lithologic intervals with distinct grain size distributions were identified. At ~11.4 ka the diatom ooze has a clear glacimarine influence which gradually decreases until ~8.2 ka. During this time interval, coincident with the early Holocene warm period, sediment is inferred to have been delivered by glacial meltwater plumes and ice-bergs in a calving bay environment. It is suggested that the glaciers in Adélie Land had retreated to their present day grounding lines by 8.2 ka, and from then on sediment was delivered to the site primarily via the Antarctic Coastal and Slope Front Currents, largely through a suspended sediment load and erosion of the surrounding banks. Enhanced biogenic mass accumulation rates and primary production at 8.2 ka suggest onset of warmer climatic conditions, coincident with the mid-Holocene Climatic Optimum. At ~4.5 ka, grain size distributions show a rapid increase in mud content coincident with a transient pulse of glacial meltwater and a sudden decrease in biogenic and terrigenous mass accumulation rates. The increased mud content is inferred to have been deposited under a reduced flow regime of the Antarctic Coastal and Slope Front Currents during the Neoglacial period that followed the final stages of deglaciation in the Ross Sea. It is hypothesised here that cessation of glacial retreat in the Ross Sea and the development of the modern day Ross Sea polynya resulted in enhanced Antarctic Surface Water production which led to increased sea ice growth in the Adélie Land region. The presence of sea ice led to reduced primary production and a decrease in the maximum current strength acting to advect coarser-sized terrigenous sediment to the core site during this time. Sedimentation rates appear to have a strong correlation with the El Niño Southern Oscillation (ENSO) over the last 8.2 kyr, and are inferred to be related to changing sea ice extent and zonal wind strength. Light laminae counts (biogenic bloom events) appear to decrease in frequency during time intervals dominated by El Niño events. Spectral analysis of the greyscale values of core photographs reveals peaks in the 2-7 year band, known ENSO periods, which increase in frequency in the mid-and-late Holocene. Spectral analyses of the sand percent and natural gamma ray (NGR, a measure of clay mineral input) content of the core reveal peaks in the ~40-60, 200-300, 600, 1200-1600 and 2200-2400 year bands. The most significant of these cycles in the NGR data is in 40-60 year band may be related to internal mass balance dynamics of the Mertz Glacier or to the expansion and contraction of the Antarctic circumpolar vortex. Cycles in the 200-300 and 2200-2400 year bands are related to known periods of solar variability, which have previously been found to regulate primary productivity in Antarctic coastal waters. Cycles in the 590-625 and 1200-1600 year bands have a strong signal through the entire record and are common features of Holocene climatic records, however the origin of these cycles is still under debate between solar forcing and an independent mode of internal ocean oscillation.</p>

Holocene sediment transport and climate variability of offshore Adélie Land, East Antarctica

<p>Grain size analysis of the terrigenous fraction of a laminated diatom ooze dating back to 11.4 kyr recovered offshore Adélie Land, East Antarctic margin was used to examine variations in sediment transport, depositional environments and Holocene climate variability at the location. Interpretations were assisted by additional proxies of primary productivity (δ¹³CFA, BSi%), glacial meltwater input (δDFA) and subsurface temperature (TEXL₈₆). Three lithologic intervals with distinct grain size distributions were identified. At ~11.4 ka the diatom ooze has a clear glacimarine influence which gradually decreases until ~8.2 ka. During this time interval, coincident with the early Holocene warm period, sediment is inferred to have been delivered by glacial meltwater plumes and ice-bergs in a calving bay environment. It is suggested that the glaciers in Adélie Land had retreated to their present day grounding lines by 8.2 ka, and from then on sediment was delivered to the site primarily via the Antarctic Coastal and Slope Front Currents, largely through a suspended sediment load and erosion of the surrounding banks. Enhanced biogenic mass accumulation rates and primary production at 8.2 ka suggest onset of warmer climatic conditions, coincident with the mid-Holocene Climatic Optimum. At ~4.5 ka, grain size distributions show a rapid increase in mud content coincident with a transient pulse of glacial meltwater and a sudden decrease in biogenic and terrigenous mass accumulation rates. The increased mud content is inferred to have been deposited under a reduced flow regime of the Antarctic Coastal and Slope Front Currents during the Neoglacial period that followed the final stages of deglaciation in the Ross Sea. It is hypothesised here that cessation of glacial retreat in the Ross Sea and the development of the modern day Ross Sea polynya resulted in enhanced Antarctic Surface Water production which led to increased sea ice growth in the Adélie Land region. The presence of sea ice led to reduced primary production and a decrease in the maximum current strength acting to advect coarser-sized terrigenous sediment to the core site during this time. Sedimentation rates appear to have a strong correlation with the El Niño Southern Oscillation (ENSO) over the last 8.2 kyr, and are inferred to be related to changing sea ice extent and zonal wind strength. Light laminae counts (biogenic bloom events) appear to decrease in frequency during time intervals dominated by El Niño events. Spectral analysis of the greyscale values of core photographs reveals peaks in the 2-7 year band, known ENSO periods, which increase in frequency in the mid-and-late Holocene. Spectral analyses of the sand percent and natural gamma ray (NGR, a measure of clay mineral input) content of the core reveal peaks in the ~40-60, 200-300, 600, 1200-1600 and 2200-2400 year bands. The most significant of these cycles in the NGR data is in 40-60 year band may be related to internal mass balance dynamics of the Mertz Glacier or to the expansion and contraction of the Antarctic circumpolar vortex. Cycles in the 200-300 and 2200-2400 year bands are related to known periods of solar variability, which have previously been found to regulate primary productivity in Antarctic coastal waters. Cycles in the 590-625 and 1200-1600 year bands have a strong signal through the entire record and are common features of Holocene climatic records, however the origin of these cycles is still under debate between solar forcing and an independent mode of internal ocean oscillation.</p>

Does glacial retreat impact benthic chironomid communities? A case study from Rocky Mountain National Park, Colorado

The aim of this study was to determine which environmental variables are responsible for modern benthic chironomid distributions in a glacial setting. The chironomid communities from nine alpine lakes were assessed, and forty-three individual taxa were extracted and identified. Surface water temperature and nitrate were strongly and negatively correlated (−0.82, p = 0.007), suggesting that glacial meltwater (the driver that explains both surface water temperature (SWT) (°C) and nitrate (NO3 + NO2-N)) is the environmental variable that explains the most variance (15%). On average, lakes receiving glacial meltwater were 2.62 °C colder and contained 66% more NO3 + NO2-N than lakes only receiving meltwater from snow. The presence of taxa from the tribe Diamesinae indicates very cold input from running water, and these taxa may be used as a qualitative indicator species for the existence of glacial meltwater within a lake catchment. Heterotrissocladius, Diamesa spp., and Pseudodiamesa were present in the coldest lakes. Chironomus, Diplocladius, and Protanypus were assemblages found in cold lakes affiliated with the littoral zone or alpine streams. The modern benthic chironomid communities collected from the alpine of subalpine lakes of Rocky Mountain National Park, Colorado, represent a range of climatic and trophic influences and capture the transition from cold oligotrophic lakes to warmer and eutrophic conditions.

Quantifying the glacial meltwater contribution to streams in mountainous regions using highly resolved stable water isotope measurements

This study aims to determine the contribution of glacial meltwater to streams in mountainous regions based on stable water isotope measurements (δ18O and δ2H). For this purpose, three partially glaciated catchments were selected as the study area in the central Swiss Alps being representative of catchments that are used for hydropower energy production in Alpine regions. The glacial meltwater contribution to the catchments’ stream discharges was evaluated based on high-resolution δ18O and δ2H measurements of the end-members that contribute to the stream discharge (ice, rain, snow) and of the discharging streams. The glacial meltwater contribution to the stream discharges could be unequivocally quantified after the snowmelt in August and September when most of the annual glacial meltwater discharge occurs. In August and September, the glacial meltwater contribution to the stream discharges corresponds to up to 95 ± 2 % and to 28.7 % ± 5 % of the total annual discharge in the evaluated catchments. The high glacial meltwater contribution demonstrates that the mountainous stream discharges in August and September will probably strongly decrease in the future due to global warming-induced deglaciation, which will be, however, likely compensated by higher discharge rates in winter and spring. Nevertheless, the changing mountainous streamflow regimes in the future will pose a challenge for hydropower energy production in the mountainous areas. Overall, this study provides a successful example of an Alpine catchment monitoring strategy to quantify the glacial meltwater contribution to stream discharges based on stable isotope water data, which leads to a better validation of existing modelling studies and which can be adapted to other mountainous regions.

Glacial Change and Its Hydrological Response in Three Inland River Basins in the Qilian Mountains, Western China

Glacial changes have great effects on regional water security because they are an important component of glacierized basin runoff. However, these impacts have not yet been integrated and evaluated in the arid/semiarid inland river basins of western China. Based on the degree-day glacier model, glacier changes and their hydrologic effects were studied in 12 subbasins in the Shiyang River basin (SYRB), Heihe River basin (HHRB) and Shule River basin (SLRB). The results showed that the glacier area of each subbasin decreased by 16.7–61.7% from 1965 to 2020. By the end of this century, the glacier areas in the three basins will be reduced by 64.4%, 72.0% and 83.4% under the three climate scenarios, and subbasin glaciers will disappear completely after the 2070s even under RCP2.6. Glacial runoff in all subbasins showed a decreasing–increasing–decreasing trend, with peak runoff experienced in 11 subbasins during 1965~2020. The contribution of glacial meltwater to total runoff in the basin ranged from 1.3% to 46.8% in the past, and it will decrease in the future due to increasing precipitation and decreasing glacial meltwater. However, the scale differences in glacier runoff are significant when aggregated over the region/basin/subbasin. This suggests that the results of large-scale generalization may be misleading for subbasin glacier water resource evaluations. Therefore, the hydrological effects of glaciers should be studied more in subbasins to provide an accurate reference for practical water resource management.

Changes in Glacial Meltwater Runoff and Its Response to Climate Change in the Tianshan Region Detected Using Unmanned Aerial Vehicles (UAVs) and Satellite Remote Sensing

The Tianshan Mountains, known as the “water tower” of Central Asia, are the major source of water for the most part of Xinjiang and oasis region of Central Asia. However, climate warming has amplified the discharges of glacial meltwater in the Tianshan Mountains. In this study, we calculated river discharge by integrating cross-sections mapped using unmanned aerial vehicles (UAV) and water velocity data collected in the field. Multiple remote sensing images, such as Landsat and Sentinel-2 imagery, were applied to estimate the long-term discharge of 19 river sections in ungauged regions of the Tianshan Mountains. River discharge variations under climate change were also examined. Using our in-situ measured discharges as reference, the UAV derived discharge results have an NSE (Nash–Sutcliffe efficiency) of 0.98, an RMSE (root mean square error) of 8.49 m3/s, and an average qualification rate of 80%. The monthly discharge of glacial meltwater-dominated river sections showed an average decrease of 2.46% during 1989–2019. The shrinking and even disappearance of mountain glaciers (approximately −4.98 km2/year) was the main reasons for the decrease trend. However, the precipitation-dominated river sections showed an average increase of 2.27% for the same period. The increase in precipitation (approximately 1.93 mm/year) was the key cause for the increase tendency. This study highlights remote sensing hydrological station technology and its application in the long-term prediction of river discharge, which is critical for decision-making regarding integrated water resource management in alpine regions.

Holocene Lake Evolution and Glacial Fluctuations Indicated by Carbonate Minerals and Their Isotopic Compositions in the Sediments of a Glacial Melt Recharge Lake on the Northwestern Tibetan Plateau

Lakes and glaciers are widely distributed on the Tibetan Plateau and are linked via hydrological processes. They are experiencing rapid changes due to global warming, but their relationships during the Holocene are less well known due to limited coupled geological records. Here, we analyzed the δ13C-VPDB and δ18O-VPDB values and ion content of calcite and aragonite in a 407-cm-long sediment core from Guozha Co, a closed basin on the northwestern Tibetan Plateau supplied by glacial meltwater, in order to understand how the lake responded to glacier changes during the Holocene. Our results indicate that the glacial meltwater lowered the lake’s temperature and the δ18Olake water and δ18Oendogenic + authigenic carbonate values and diluted the ion concentrations in the lake water. Three stages of evolution, 8.7–4.0, 4.0–1.5, and 1.5 kyr BP to present, are distinguished based on the decrease in glacial meltwater recharge. Guozha Co has been a closed basin since at least 8.7 kyr BP, and it has changed from a fresh water lake during 8.7–1.5 kyr BP to a brackish lake from 1.5 kyr BP to present due to several climate events. The famous 4.2 kyr BP cold event was identified in the core at 4.0 kyr BP, while warm events occurred at 6.2, 3.9, 2.2, 0.9, and 0.4 kyr BP. Both glaciers and lakes in this area are controlled by climate, but they exhibit opposite changes, that is, glaciers retreat and lakes expand, and vice versa. Our results provide an accurate interpretation of the cold events based on carbonate minerals and carbon–oxygen isotopes in glacial meltwater–recharged lake sediments.