Gases in ice cores

Subsurface In Situ Detection of Microbes and Diverse Organic Matter Hotspots in the Greenland Ice Sheet

We used a deep-ultraviolet fluorescence mapping spectrometer, coupled to a drill system, to scan from the surface to 105 m depth into the Greenland ice sheet. The scan included firn and glacial ice and demonstrated that the instrument is able to determine small (mm) and large (cm) scale regions of organic matter concentration and discriminate spectral types of organic matter at high resolution. Both a linear point cloud scanning mode and a raster mapping mode were used to detect and localize microbial and organic matter "hotspots" embedded in the ice. Our instrument revealed diverse spectral signatures. Most hotspots were <20 mm in diameter, clearly isolated from other hotspots, and distributed stochastically; there was no evidence of layering in the ice at the fine scales examined (100 μm per pixel). The spectral signatures were consistent with organic matter fluorescence from microbes, lignins, fused-ring aromatic molecules, including polycyclic aromatic hydrocarbons, and biologically derived materials such as fulvic acids. In situ detection of organic matter hotspots in ice prevents loss of spatial information and signal dilution when compared with traditional bulk analysis of ice core meltwaters. Our methodology could be useful for detecting microbial and organic hotspots in terrestrial icy environments and on future missions to the Ocean Worlds of our Solar System.

Cryosphere Services and Human Well-Being

Cryosphere services (CSs) refer to various benefits that humans directly or indirectly obtain from the cryosphere, which makes significant contributions to human well-being (HWB). To facilitate such research, we first present a classification system for conceptualizing, monitoring and assessing CSs based on the current process-based understanding of their nature and sustainability. Specifically, the CSs are grouped into five major categories (provisioning, regulating, cultural, bearing and supporting services) and 18 sub-categories. Then we provide a detailed overview on formation, current status and anticipated future changes of the identified types of the services, and their impact on HWB. Finally, the spatio-temporal scales, the links of the services with HWB and climate-dependence are further discussed. The research of CSs adopt interdisciplinary approach to address the formation mechanisms of CSs and their dynamic relationships with HWB, which is poised to provide a better understanding of the cryosphere’s role in human society and help enhance socio-ecological sustainability and HWB over cryosphere-affected areas. Notably, most CSs have been deteriorating under global warming and cryosphere shrinkage, further leading to negative impacts on associated HWB. Therefore, great attention should be paid to the changes in CSs and their cascading risks.

Microbial metabolism directly affects trace gases in (sub) polar snowpacks

Concentrations of trace gases trapped in ice are considered to develop uniquely from direct snow/atmosphere interactions at the time of contact. This assumption relies upon limited or no biological, chemical or physical transformations occurring during transition from snow to firn to ice; a process that can take decades to complete. Here, we present the first evidence of environmental alteration due to in situ microbial metabolism of trace gases (methyl halides and dimethyl sulfide) in polar snow. We collected evidence for ongoing microbial metabolism from an Arctic and an Antarctic location during different years. Methyl iodide production in the snowpack decreased significantly after exposure to enhanced UV radiation. Our results also show large variations in the production and consumption of other methyl halides, including methyl bromide and methyl chloride, used in climate interpretations. These results suggest that this long-neglected microbial activity could constitute a potential source of error in climate history interpretations, by introducing a so far unappreciated source of bias in the quantification of atmospheric-derived trace gases trapped within the polar ice caps.

The term ‘Anthropocene’ in the context of formal geological classification

In recent years, ‘Anthropocene’ has been proposed as an informal stratigraphic term to denote the current interval of anthropogenic global environmental change. A case has also been made to formalize it as a series/epoch, based on the recognition of a suitable marker event, such as the start of the Industrial Revolution in northern Europe. For the Anthropocene to merit formal definition, a global signature distinct from that of the Holocene is required that is marked by novel biotic, sedimentary and geochemical change. Although there is clear evidence of anthropogenic effects in geological sequences, it is uncertain whether these trends are sufficiently distinct, consistent and dated for the proposal for a Holocene/Anthropocene boundary to be substantiated. The current view of the Earth-Science community is that it should remain informal. For formal definition a Global Stratigraphic Section and Point (GSSP) is required. Adoption of the term ‘Anthropocene’ will ultimately depend on recognition of a global event horizon. Without this, there is no justification for decoupling the Anthropocene from the Holocene. If the Anthropocene is deemed to have utility, it should be as an informal historical designation rather than a formally defined stratigraphic unit (of whatever status) within the geological timescale.