January 2016 extensive summer melt in West Antarctica favoured by strong El Niño

Multiscale Temporal Variations of Atmospheric Mercury Distinguished by the Hilbert-Huang Transform Analysis Reveals Multiple El Niño-Southern Oscillation Links

Atmospheric mercury (Hg) cycling is sensitive to climate-driven changes, but links with various teleconnections remain unestablished. Here, we revealed the El Niño-Southern Oscillation (ENSO) influence on gaseous elemental mercury (GEM) concentrations recorded at a background station in East Asia using the Hilbert-Huang transform (HHT). The timing and magnitude of GEM intrinsic variations were clearly distinguished by ensemble empirical mode decomposition (EEMD), revealing the amplitude of the GEM concentration interannual variability (IAV) is greater than that for diurnal and seasonal variability. We show that changes in the annual cycle of GEM were modulated by significant IAVs at time scales of 2-7 years, highlighted by a robust GEM IAV-ENSO relationship of the associated intrinsic mode functions. With confirmation that ENSO modulates the GEM annual cycle, we then found that weaker GEM annual cycles may have resulted from El Niño-accelerated Hg evasion from the ocean. Furthermore, the relationship between ENSO and GEM is sensitive to extreme events (i.e., 2015-2016 El Niño), resulting in perturbation of the long-term trend and atmospheric Hg cycling. Future climate change will likely increase the number of extreme El Niño events and, hence, could alter atmospheric Hg cycling and influence the effectiveness evaluation of the Minamata Convention on Mercury.

Interannual variations in meltwater input to the Southern Ocean from Antarctic ice shelves

Ocean-driven basal melting of Antarctica's floating ice shelves accounts for about half of their mass loss in steady-state, where gains in ice shelf mass are balanced by losses. Ice shelf thickness changes driven by varying basal melt rates modulate mass loss from the grounded ice sheet and its contribution to sea level, and the changing meltwater fluxes influence climate processes in the Southern Ocean. Existing continent-wide melt rate datasets have no temporal variability, introducing uncertainties in sea level and climate projections. Here, we combine surface height data from satellite radar altimeters with satellite-derived ice velocities and a new model of firn-layer evolution to generate a high-resolution map of time-averaged (2010-2018) basal melt rates, and time series (1994-2018) of meltwater fluxes for most ice shelves. Total basal meltwater flux in 1994 (1090±150 Gt/yr) was not significantly different from the steady-state value (1100±60 Gt/yr), but increased to 1570±140 Gt/yr in 2009, followed by a decline to 1160±150 Gt/yr in 2018. For the four largest "cold-water" ice shelves we partition meltwater fluxes into deep and shallow sources to reveal distinct signatures of temporal variability, providing insights into climate forcing of basal melting and the impact of this melting on the Southern Ocean.

Spatio-temporal changes and prediction of Amery ice shelf, east Antarctica: A remote sensing and statistics-based approach

The Amery ice shelf (AIS) dynamics and mass balance play key role to decipher changes in the global climate scenario. The spatio-temporal changes in morphology of the AIS were studied into a number of transects at 5 km uniform intervals using multi-dated Moderate Resolution Imaging Spectro-radiometer (MODIS) satellite data (2001-2016) of the austral summer months (January-March). Past ice shelf extents have been reconstructed and future ice shelf extents were estimated for 5- and 10-year time periods. The rate changes of AIS extent were estimated using the linear regression analysis and cross-validated with the coefficient of determination (R²) and root-mean-square error (RMSE) methods. Further, the changes in shelf extent were linked to prevailing factors viz. mass changes, Southern Annular Mode (SAM) index, and ocean-air temperatures. The study reveals that the AIS extent has been prograded at the rate of 994 m/year with an average 14.5 km increase in the areal extents during 2001-2016, as compared to the year 2001, whereas, the maximum advancement in ice shelf extent was recorded during the 2006-2016 period. Based on the linear regression analysis, the predicted ice shelf extents (i.e., the summer 2021 and 2016) show progradation in all the transects. About 52% of transects exhibit ±200 m RMSE values, indicating better agreement between the estimated and satellite-based ice-shelf position. The recent changes (2017-2019) observed in the ice shelf are cross validated with predicted ice self-extent rates. The eastern part of Mackenzie Bay to Ingrid Christensen coast recorded advancement in the ice shelf extents and mass which is the feedback of positive SAM along with a decrease in the temperatures (air temperature and sea surface temperature). The present study demonstrates that the combined use of satellite imagery and statistical techniques can be useful in quantifying and predicting ice shelf morphological variability.

Remote Sensing of Environmental Changes in Cold Regions: Methods, Achievements and Challenges

Cold regions, including high-latitude and high-altitude landscapes, are experiencing profound environmental changes driven by global warming. With the advance of earth observation technology, remote sensing has become increasingly important for detecting, monitoring, and understanding environmental changes over vast and remote regions. This paper provides an overview of recent achievements, challenges, and opportunities for land remote sensing of cold regions by (a) summarizing the physical principles and methods in remote sensing of selected key variables related to ice, snow, permafrost, water bodies, and vegetation; (b) highlighting recent environmental nonstationarity occurring in the Arctic, Tibetan Plateau, and Antarctica as detected from satellite observations; (c) discussing the limits of available remote sensing data and approaches for regional monitoring; and (d) exploring new opportunities from next-generation satellite missions and emerging methods for accurate, timely, and multi-scale mapping of cold regions.

Ice sheets matter for the global carbon cycle

The cycling of carbon on Earth exerts a fundamental influence upon the greenhouse gas content of the atmosphere, and hence global climate over millennia. Until recently, ice sheets were viewed as inert components of this cycle and largely disregarded in global models. Research in the past decade has transformed this view, demonstrating the existence of uniquely adapted microbial communities, high rates of biogeochemical/physical weathering in ice sheets and storage and cycling of organic carbon (>104 Pg C) and nutrients. Here we assess the active role of ice sheets in the global carbon cycle and potential ramifications of enhanced melt and ice discharge in a warming world.

Dynamical and Thermodynamical Influences of the Maritime Continent on ENSO Evolution

El Niño-Southern Oscillation (ENSO) exerts tremendous influences on the global climate. Through dynamic lifting and thermal forcing, the Maritime Continent (MC) plays an important role in affecting global atmospheric circulation. In spite of the extensive studies on ENSO mechanisms, the influence of MC on the characteristics of ENSO life cycle remains unclear. Our coupled model experiments reveal that the absence of the MC land contributes to a strong ENSO asymmetry and a weakened nonlinear atmospheric response to the combined seasonal and interannual SST variations (i.e. the combination mode) that prolongs the warm events, resulting in a reduction of ENSO frequency. On the other hand, our experiments suggest that the global climate model applied (NCAR CESM) overestimates the MC topographic uplifting effect on ENSO simulation. Overall, this study provides a new physical insight into the nature of the MC influence on ENSO evolution.

The Springtime Influence of Natural Tropical Pacific Variability on the Surface Climate of the Ross Ice Shelf, West Antarctica: Implications for Ice Shelf Thinning

Observational records starting in the 1950s show West Antarctica is amongst the most rapidly warming regions on the planet. Together with increased intrusions of warm circumpolar deep water (CDW) onto the continental shelf due to local wind forcing (the primary mechanism in recent decades), this has resulted in enhanced surface and basal melting of floating ice shelves and an associated acceleration and thinning of West Antarctic outlet glaciers, increasing the rate of global sea level rise. In this study, it is shown that during the austral spring season, significant surface warming across West Antarctica has shifted westward to the Ross Ice Shelf in recent decades in response to enhanced cyclonic circulation over the Ross Sea. These circulation changes are caused by a Rossby wave train forced by increasing sea surface temperatures in the western tropical Pacific, which is tied to the springtime shift of the Interdecadal Pacific Oscillation (IPO) to its negative phase after 1992. While the local wind trends enhance warm air advection and surface warming across the Ross Ice Shelf, the strong easterly component of the wind trends reduces the likelihood for intrusions of CDW onto the continental shelf in this region. This suggests that during spring there are competing mechanisms of surface and basal melting of the Ross Ice Shelf, both of which are closely tied to natural tropical Pacific decadal variability. Moreover, that the projected transition of the IPO back to its positive phase in the coming decade, though likely to reduce surface warming on the Ross Ice Shelf, could increase the risk of disintegration of Ross Sea ice shelves due to increased intrusions of CDW and enhanced basal melting.

Direct and Indirect Effects of Penguin Feces on Microbiomes in Antarctic Ornithogenic Soils

Expansion of penguin activity in maritime Antarctica, under ice thaw, increases the chances of penguin feces affecting soil microbiomes. The detail of such effects begins to be revealed. By comparing soil geochemistry and microbiome composition inside (one site) and outside (three sites) of the rookery, we found significant effects of penguin feces on both. First, penguin feces change soil geochemistry, causing increased moisture content (MC) of ornithogenic soils and nutrients C, N, P, and Si in the rookery compared to non-rookery sites, but not pH. Second, penguin feces directly affect microbiome composition in the rookery, not those outside. Specifically, we found 4,364 operational taxonomical units (OTUs) in 404 genera in six main phyla: Proteobacteria, Actinobacteria, Gemmatimonadetes, Acidobacteria, Chloroflexi, and Bacteroidetes. Although the diversity is similar among the four sites, the composition is different. For example, penguin rookery has a lower abundance of Acidobacteria, Chloroflexi, and Nitrospirae but a higher abundance of Bacteroidetes, Firmicutes, and Thermomicrobia. Strikingly, the family Clostridiaceae of Firmicutes of penguin-feces origin is most abundant in the rookery than non-rookery sites with two most abundant genera, Tissierella and Proteiniclasticum. Redundancy analysis showed all measured geochemical factors are significant in structuring microbiomes, with MC showing the highest correlation. We further extracted 21 subnetworks of microbes which contain 4,318 of the 4,364 OTUs using network analysis and are closely correlated with all geochemical factors except pH. Our finding f penguin feces, directly and indirectly, affects soil microbiome suggests an important role of penguins in soil geochemistry and microbiome structure of maritime Antarctica.