Ocean Currents, Jet Streams, and Polar Bears

This chapter is divided into four sections, describing various impacts of glacier melt on different Earth ecosystems, including the effects of melting ice and water temperature on changes to ocean currents, on the global air Jet Stream, and on land surfaces, such as the popping up effect (the surface rebound effect) of the Earth once glaciers recede. It discusses the role of glacier meltwater for energy generation, as well as the impacts of the acceleration of glacier melt on flora and fauna, such as polar bears, salmon, and river bed and riparian biota.

Regional-scale phytoplankton dynamics and their association with glacier meltwater runoff in Svalbard

Arctic amplification of global warming has accelerated mass loss of Arctic land ice over the past decades and lead to increased freshwater discharge into glacier fjords and adjacent seas. Glacier freshwater discharge is typically associated with high sediment loads which limits the euphotic depth, but may also provide surface waters with essential nutrients, thus having counter-acting effects on marine productivity. In-situ observations from a few measured fjords across the Arctic indicate that glacier fjords dominated by marine-terminating glaciers are typically more productive than those with only land-terminating glaciers. Here we combine chlorophyll a from satellite ocean colour, an indicator of phytoplankton biomass, with glacier meltwater runoff from climatic mass-balance modelling to establish a statistical model of summertime-phytoplankton dynamics in Svalbard (mid-June to September). Statistical analysis reveals positive spatiotemporal association of chlorophyll a with glacier runoff for 7 out of 14 primary hydrological regions. These regions consist predominantly of the major fjord systems of Svalbard. The adjacent land areas are characterized by a wide range of total glacier coverage (35.5 % to 81.2 %) and fraction of marine-terminating glacier area (40.2 % to 87.4 %). We find that an increase in specific glacier-runoff rate of 10 mm water equivalent per 8-day timeperiod raises summertime chlorophyll a concentrations by 5.2 % to 20.0 %, depending on region. During the annual peak discharge we estimate that glacier runoff contributes to 13.1 % to 50.2 % increase in chlorophyll a compared to situations with no runoff. This suggest that glacier runoff is an important factor sustaining summertime phytoplankton production in Svalbard fjords, in line with findings from several fjords in Greenland. In contrast, for regions bordering open coasts, and beyond 10 km distance from the shore, we do not find significant association of chlorophyll a with runoff. In these regions, physical ocean and sea ice variables control chlorophyll a, pointing at the importance of a late sea ice breakup in northern Svalbard, as well as the advection of Atlantic water masses along the West Spitsbergen Current for summertime phytoplankton dynamics. Our method allows for investigation and monitoring of glacier-runoff effects on primary production throughout the summer season and is applicable on a Pan-Arctic scale, thus complementing valuable but scarce in-situ measurements in both space and time.

Remote Sensing Investigation of the Offset Effect between Reservoir Impoundment and Glacier Meltwater Supply in Tibetan Highland Catchment

This article presents multi-source remote sensing measurements to quantify the water impoundment and regulation of the Zhikong Reservoir (ZKR) and Pangduo Reservoir (PDR), together with the estimation of the glacier mass balance to explore whether the increased glacier meltwater supply can buffer the influences of the reservoir impoundment to some degree in the Tibetan highland catchment. The ZKR and PDR are two reservoirs constructed on the upper Lhasa River that originate from the Nyainqentanglha glaciers in the remote headwater in the Tibetan Plateau (TP) and lacks historical in situ hydrological observations in the long term. Therefore, the Joint Research Center (JRC) Global Surface Water dataset (GSW), and the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) data were used for estimating the total amount of water storage of the two reservoirs, and the SRTM and TanDEM-X DEMs were used for estimating the glacier mass balance. The result shows that the total amount of water impounded by reservoirs is 0.76 Gt, roughly 54% of their design capacities. The mass balance of the glaciers is estimated by comparing the elevation changes between the SRTM and TanDEM-X DEMs. The glaciers in this region melt at an average rate of 0.09 ± 0.02 Gt·year−1 from 2000 to circa 2013, and the impounded water of these reservoirs is comparable to the amount of glacier-fed meltwater in eight years.

Anthropogenic water depletion in the Indo-Gangetic Plain

<p>The Indo-Gangetic Plain, feeding more than 9 billion people, are facing serious water scarcity due to expanding populations and development in agriculture and industry. Rainfall concentrated in monsoon season, about 70% of precipitation falls between June and September, causes the imbalance between water supply and demand. A large amount of groundwater is extracted for irrigation during dry season, causes the groundwater to decline. Increasing glacier meltwater under the ongoing warming of global climate from upstream high mountainous also modulates the variation of terrestrial water storage (TWS) in this region. Thus, estimating and evaluating anthropogenic water depletion are beneficial to water resources protection and management in the Indo-Gangetic Plain.</p><p>Here, we propose a method to remove the influence of climate variability and obtain human-driven TWS variability. Atmosphere-driven TWS variability is estimated by a relationship between change in TWS (GRACE data) and precipitation and temperature, which has been confirmed that these two variables (precipitation and temperature) already explain a substantial fraction of continental-scale run off dynamics in previous studies. Glacier melting recharge from upstream high mountainous is calculated by the proportion with the temperature.</p><p>Results show that the rate of anthropogenic depletion of water in Indus Plain increased from -5.5 km<sup>3</sup>/yr to -25.0 km<sup>3</sup>/yr during 2003 - 2011 due to the deficient precipitation, and remained stable from 2011 to 2016 at the rate of ~-26.0 km<sup>3</sup>/yr with increasing precipitation and enhancing glacier meltwater recharge. The rate of anthropogenic depletion of water in Ganges Plain (including the Brahmaputra River) slowed from -37.7 km<sup>3</sup>/yr to -12.0 km<sup>3</sup>/yr during 2003 -2011due to the increased glacier meltwater recharge, which reduced the pressure of irrigation water in northwest of the Plain. However, with the increasing temperature since 2014, The rate of anthropogenic depletion of water increased to -20.0 km<sup>3</sup>/yr in 2016.</p>

Groundwater–glacier meltwater interaction in proglacial aquifers

Groundwater plays a significant role in glacial hydrology and can buffer changes to the timing and magnitude of flows in meltwater rivers. However, proglacial aquifer characteristics or groundwater dynamics in glacial catchments are rarely studied directly. We provide direct evidence of proglacial groundwater storage, and quantify multi-year groundwater–meltwater dynamics, through detailed aquifer characterisation and intensive high-resolution monitoring of the proglacial system of a rapidly retreating glacier, Virkisjökull, in south-eastern Iceland. Proglacial unconsolidated glaciofluvial sediments comprise a highly permeable aquifer (25–40 m d−1) in which groundwater flow in the shallowest 20–40 m of the aquifer is equivalent to 4.5 % (2.6 %–5.8 %) of mean river flow, and 9.7 % (5.8 %–12.3 %) of winter flow. Estimated annual groundwater flow through the entire aquifer thickness is 10 % (4 %–22 %) the magnitude of annual river flow. Groundwater in the aquifer is actively recharged by glacier meltwater and local precipitation, both rainfall and snowmelt, and strongly influenced by individual precipitation events. Local precipitation represents the highest proportion of recharge across the aquifer. However, significant glacial meltwater influence on groundwater within the aquifer occurs in a 50–500 m river zone within which there are complex groundwater–river exchanges. Stable isotopes, groundwater dynamics and temperature data demonstrate active recharge from river losses, especially in the summer melt season, with more than 25 % and often >50 % of groundwater in the near-river aquifer zone sourced from glacier meltwater. Proglacial aquifers such as these are common globally, and future changes in glacier coverage and precipitation are likely to increase the significance of groundwater storage within them. The scale of proglacial groundwater flow and storage has important implications for measuring meltwater flux, for predicting future river flows, and for providing strategic water supplies in de-glaciating catchments.