When, How, and Why Did the West Antarctic Ice Sheet Retreat in the Ross Sea Since the Last Glacial Maximum Using Foraminiferal And Porewater Geochemistry

The Antarctic Ice Sheets (AIS) began to retreat from their Last Glacial Maximum (LGM) position sometime after 19,000 years ago. However, the corrosive waters circulating around Antarctica has prevented the recovery of radiocarbon-dateable material, hindering the development of deglacial chronologies. During Expedition NBP1502B to the eastern Ross Sea, an unprecedented quantity of fossil foraminifera and bivalves were recovered. Radiocarbon-dated specimens have been used to constrain the timing of West-AIS retreat from Whales Deep basin and Ross Bank. Whales Deep samples show that the WAIS retreated from its LGM position on the continental shelf edge by 14,700 ± 400 calibrated radiocarbon years ago (cal yr BP). Additional ages, seafloor geomorphology and core sedimentology show that the WAIS paused several times before rapidly retreating south of the modern Ross Ice Shelf 11,500 ± 300 cal yr BP. These retreat events are concomitant with Meltwater Pulse -1a and -1b suggesting these two rapid sea-level rise events played a primary role. This finding potentially resolves a point of contention amongst Antarctic scientists. An additional factor influencing ice sheet retreat includes subglacial meltwater hydrology. Subglacial meltwater generation and drainage may have significantly influenced retreat of Antarctic ice streams in the past and at present. Oxygen isotope ratios (δ18O) from porewater recovered from Whales Deep Basin sediment cores are characteristic of modern Ross Sea waters indicating that fresh meltwater was not preserved in subglacial or glaciomarine sediment. This suggests that subglacial meltwater hydrology did not significantly affect the early stages of WAIS retreat in the Whales Deep Basin. Ross Bank – a seamount rising to 174 meters below sea level – is covered with a thin layer of pelagic sediment. A box core recovered an abundance of calcareous fossils. Radiocarbon ages indicate that the Ross Ice Shelf was grounded on Ross Bank until ~600 cal yr BP when it retreated to its present position. This is significant because it suggests that three topographic features acted to buttress the Ross Ice Shelf up until the last few centuries. Since unpinning, there are only two features, Roosevelt Island and Ross Island, that stabilize the modern Ross Ice Shelf calving front

Transcending Scale Dependence in Identifying Habitat with Resource Selection Functions

Multi-scale resource selection modeling is used to identify factors that limit species distributions across scales of space and time. This multi-scale nature of habitat suitability complicates the translation of inferences to single, spatial depictions of habitat required for conservation of species. We estimated resource selection functions (RSFs) across three scales for a threatened ungulate, woodland caribou (Rangifer tarandus caribou), with two objectives: (1) to infer the relative effects of two forms of anthropogenic disturbance (forestry and linear features) on woodland caribou distributions at multiple scales and (2) to estimate scale-integrated resource selection functions (SRSFs) that synthesize results across scales for management-oriented habitat suitability mapping. We found a previously undocumented scale-specific switch in woodland caribou response to two forms of anthropogenic disturbance. Caribou avoided forestry cut-blocks at broad scales according to first-and second-order RSFs and avoided linear features at fine scales according to third-order RSFs, corroborating predictions developed according to predator-mediated effects of each disturbance type. Additionally, a single SRSF validated as well as each of three single-scale RSFs when estimating habitat suitability across three different spatial scales of prediction. We demonstrate that a single SRSF can be applied to predict relative habitat suitability at both local and landscape scales in support of critical habitat identification and species recovery

College and University Governance: The University of Iowa Governing Board’s Selection of a President

The article reports how Bruce Harreld, one of four finalists identified by the search committee for the presidency of the University of Iowa, addressed a town hall meeting of the university community on September 1, 2015. On September 23, the Faculty Assembly of the College of Liberal Arts and Sciences, the elected representative body of the college\u27s faculty, endorsed the faculty senate\u27s vote of no confidence

A Centuries-Long Delay between a Paleo-Ice-Shelf Collapse and Grounding-Line Retreat in the Whales Deep Basin, Eastern Ross Sea, Antarctica

Recent thinning and loss of Antarctic ice shelves has been followed by near synchronous acceleration of ice flow that may eventually lead to sustained deflation and significant contraction in the extent of grounded and floating ice. Here, we present radiocarbon dates from foraminifera that constrain the time elapsed between a previously described paleo-ice-shelf collapse and the subsequent major grounding-line retreat in the Whales Deep Basin (WDB) of eastern Ross Sea. The dates indicate that West Antarctic Ice Sheet (WAIS) grounding-line retreat from the continental shelf edge was underway prior to 14.7 ± 0.4 cal kyr BP. A paleo-ice-shelf collapse occurred at 12.3 ± 0.2 cal kyr BP. The grounding position was maintained on the outer-continental shelf until at least 11.5 ± 0.3 cal kyr BP before experiencing a 200-km retreat. Given the age uncertainties, the major grounding-line retreat lagged ice-shelf collapse by at least two centuries and by as much as fourteen centuries. In the WDB, the centuries-long delay in the retreat of grounded ice was partly due to rapid aggradational stacking of an unusually large volume of grounding-zone-wedge sediment as ice-stream discharge accelerated following ice-shelf collapse. This new deglacial reconstruction shows that ongoing changes to ice shelves may trigger complex dynamics whose consequences are realized only after a significant lag

Genomic and Chemical Diversity in <i>Cannabis</i>

<p>Plants of the <i>Cannabis</i> genus are the only prolific producers of phytocannabinoids, compounds that strongly interact with the evolutionarily ancient endocannabinoid receptors shared by most bilaterian taxa. For millennia, the plant has been cultivated not only for these compounds, but also for food, rope, paper, and clothing. Today, specialized varieties yielding high-quality textile fibers, nutritional seed oil, or high cannabinoid content are cultivated across the globe. However, the genetic identities and histories of these diverse populations remain largely obscured. We analyzed the nuclear genomic diversity among 340 <i>Cannabis</i> varieties, including fiber and seed oil hemp, high cannabinoid drug-types, and feral populations. These analyses demonstrate the existence of at least three major groups of diversity with European hemp varieties more closely related to narrow leaflet drug-types (NLDTs) than to broad leaflet drug-types (BLDTs). The BLDT group appears to encompass less diversity than the NLDT, which reflects the larger geographic range of NLDTs, and suggests a more recent origin of domestication of the BLDTs. As well as being genetically distinct, hemp, NLDT, and BLDT genetic groups produce unique cannabinoid and terpenoid content profiles. This combined analysis of population genomic and trait variation informs our understanding of the potential uses of different genetic variants for medicine and agriculture, providing valuable insights and tools for a rapidly emerging valuable industry.</p

Appendix A. Defining seasons according to migration parameters.

Defining seasons according to migration parameters

Appendix B. Description of GIS-based spatial resource data.

Description of GIS-based spatial resource data

Appendix E. Area-adjusted frequencies of validation locations within ordinal bins of SRSF-predicted values per scale, population, and season.

Area-adjusted frequencies of validation locations within ordinal bins of SRSF-predicted values per scale, population, and season

Appendix C. Resource selection functions for three orders of selection, nine populations, and two seasons.

Resource selection functions for three orders of selection, nine populations, and two seasons