How do you measure ice loss in Antarctica?

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by Emil Morhardt

In a new paper about accelerated ice loss in Antarctica, Rignot et al. (2019) list the three ways: 1. the component method in which whatever data on ice and snow amounts are available at the finest resolution possible, from the smallest areas studied areas (as little as 100 meters, ranging up to 1km) are collected then added up for as many years as they are available, and the trend plotted; 2. The altimetry method which, I presume, uses satellite altimetry to figure out how much ice and snow are present based on the height above ground and sea is measured…this has a spatial resolution of 1-10km; and 3.  The gravity method (probably using the Grace satellite pairs to measure gravity changes over time owing to ice loss. The latter method can resolve centimeter-level losses but at a low resolution of 333 km. The latter two methods are relatively easy…just process satellite data…or maybe not so easy but relatively so. The component method is labor intensive, but better at pinpointing areas of loss which facilitates trying to understand what is causing the loss. Rignot used the component method.

Their results, reported widely in the news media, should be chilling.  The climate-change enhanced westerly winds in the southern hemisphere are evidently pushing relatively warm circumpolar deep water (CDW) up against the edges of the ice sheets over much of the continent and increasing their melting and calving of icebergs at much higher rates than in previous decades. The loss of ice not only increases sea level faster than anyone had thought, it allows glaciers to flow into the sea faster as well, speeding the whole process.

Not that this comes as too much of a surprise to those of us who have been following global warming, but considering the exacerbated coastal flooding that is becoming commonplace, it might be good to point out to the climate change deniers inhabiting the higher levels of our government.

Rignot et al. 2019, http://www.pnas.org/cgi/doi/10.1073/pnas.1812883116

Antarctic Sea Ice Changes Affect Krill, the Marine Food Base

by Cameron Lukos

Flores et al. 2013, hoped to create a synoptic investigation that showed seasonal changes in depth distribution of macrozooplankton and micronekton and their relationship to environment. They used data from three different expeditions that were part of a larger multi-year experiment that sailed the Lazzarev Sea collecting data on Antarctic krill in the Lazzarev Sea, creating an inventory of the pelagic macrozooplankton and micronekton from the surface down to 3000 meters, and exploring the seasonal changes in depth distribution and the relationship between communities and environmental drivers. The samples were collected via trawl nets at varying depths up to 3000 m and were done at different times of the year in order to run statistical analysis. Flores et al. found that the majority of the species sampled were found in the deep layer at depths that have not previously been studied, but there also was a higher number of species in the epipelagic layer than has been previously recorded. The higher richness in the epipelagic layer may confirm that the differences in species composition were caused by higher sampling effort or by species avoiding the surface layer. When the authors compared seasons with depth layer there were significant differences. In one instance there was a large dissimilarity between the surface layer and the overlapping epipelagic layer in each season.

Flores H., Hunt B., Kruse S., Pakhomov E., Siegel V., van Franeker J., Strass., Van de Putte A., Meesters E., Bathmann U., 2014. Seasonal Changes in the Vertical Distribution and Community Structure of Antarctic Macrozooplankton and Micronekton. Deep- Sea Research 1 84, 127–141. http://goo.gl/DB72rX

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