Platinum group element geochemistry of komatiites from the Alexo and Pyke Hill areas, Ontario, Canada

Thirty-three whole-rock drill core samples and thirteen olivine, chromite, and sulfide separates from three differentiated komatiite lava flows at Alexo and Pyke Hill, Canada, were analyzed for PGEs using the Carius tube digestion ID-ICP-MS technique. The emplaced lavas are Al-undepleted komatiites with ∼27% MgO derived by ∼50% partial melting of LILE-depleted Archean mantle. Major and minor element variations during and after emplacement were controlled by 30 to 50% fractionation of olivine Fo_93-94. The emplaced lavas are characterized by (Pd/Ir)_N = 4.0 to 4.6, (Os/Ir)_N = 1.07, and Os abundances of ∼2.3 ppb. Variations in PGE abundances within individual flows indicate that Os and Ir were compatible (bulk D_Os,Ir = 2.4-7.1) and that Pt and Pd were incompatible (bulk D_Pt,Pd < 0.2) during lava differentiation, whereas bulk D_Ru was close to unity. Analyses of cumulus olivine separates indicate that PGEs were incompatible in olivine (D_PGEs^Ol-Liq = 0.04-0.7). The bulk fractionation trends cannot be accounted for by fractionation of olivine alone, and require an unidentified Os-Ir-rich phase. The composition of the mantle source (Os = 3.9 ppb, Ir = 3.6 ppb, Ru = 5.4 ppb, Pt and Pd = 5.7 ppb) was constrained empirically for Ru, Pt, and Pd; the Os/Ir ratio was taken to be identical to that in the emplaced melt, and the Ru/Ir ratio was taken to be chondritic, so that the absolute IPGE abundances of the source were determined by Ru. This is the first estimate of the PGE composition of a mantle source derived from analyses of erupted lavas. The suprachondritic Pd/Ir and Os/Ir of the inferred Abitibi komatiite mantle source are similar to those in off-craton spinel lherzolites, orogenic massif lherzolites, and enstatite chondrites, and are considered to be an intrinsic mantle feature. Bulk partition coefficients for use in komatiite melting models derived from the source and emplaced melt compositions are: D_Os,Ir = 2.3, D_Ru = 1.0, D_Pt,Pd = 0.07. Ruthenium abundances are good indicators of absolute IPGE abundances in the mantle sources of komatiite melts with 26 to 29% MgO, as Ru fractionates very little during both high degrees of partial melting and lava differentiation.     

Preliminary investigation of a late Wisconsinan fauna from K1 cave, Queen Charlotte Islands (Haida Gwaii), Canada

Recent investigations of a limestone solution cave on the Queen Charlotte Islands (Haida Gwaii) have yielded skeletal remains of fauna including late Pleistocene and early Holocene bears, one specimen of which dates to ca. 14,400 ¹⁴C yr B.P. This new fossil evidence sheds light on early postglacial environmental conditions in this archipelago, with implications for the timing of early human migration into the Americas.     

Closely related thyasirid bivalves associate with multiple symbiont phylotypes

Species of thyasirid bivalves are considered to be representative of early stages of chemosymbiosis, given that bacterial symbionts occur outside gill epithelial cells, vary among species in their abundance and nutritional importance, and are environmentally acquired. For these reasons, assessing the extent of host–symbiont specificity in thyasirids could provide valuable information on the evolution of chemosymbiosis. We show that individuals of two closely related and sympatric Thyasira cf. gouldi operational taxonomic units collected from three sites in a fjord in Newfoundland, Canada, associate with one of three distinct, closely related symbiont phylotypes. While associations show some site‐specificity, there is flexibility in host–symbiont pairings within the fjord, further supporting an early and relatively unspecific stage of chemosymbiosis in this family. Morphologic differences observed both within and among symbiont phylotypes suggest physiologic variation, possibly induced by small‐scale differences in sedimentary conditions.     

Submergence and Herbivory as Divergent Causes of Marsh Loss in Long Island Sound

Tidal marsh degradation has been attributed to a number of different causes, but few studies have examined multiple potential factors at the same sites. Differentiating the diverse drivers of marsh loss is critical to prescribing successful interventions for conservation and restoration of this important habitat. We evaluated two hypotheses for vegetation loss at two marshes in Long Island Sound (LIS): (1) marsh submergence, caused by an imbalance between sea-level rise and marsh accretion, and (2) defoliation associated with herbivory by the purple marsh crab, Sesarma reticulatum. At our western LIS site, we found no evidence of herbivory: crabs were scarce, and crab-exclusion cages provided no benefit. We attribute degradation at that site to submergence, a conclusion supported by topographic and hydrologic data showing that loss of vegetation occurred only in wetter parts of the marsh. In contrast, at our central LIS site, our observations were consistent with herbivory as a driving force: There were substantial populations of Sesarma, crab-exclusion cages allowed plants to thrive, and vegetation loss took place across a variety of elevations. We also analyzed soil conditions at both sites, in order to determine the signatures of different degradation processes and assess the potential for restoration. At the submergence site, unvegetated soils exhibited high bulk density, low organic content, and low soil strength, posing significant biogeochemical challenges to re-colonization by vegetation. At the herbivory site, unvegetated soils had a characteristic “riddled-peat” appearance, resulting from expansion and erosion of Sesarma burrow networks. The high redox potential and organic content of those soils suggested that revegetation at the herbivory site would be likely if Sesarma populations could be controlled before erosion leads to elevation loss.     

Floodgate Operations and Fish Communities in Tidal Creeks of the Lower Fraser River (British Columbia,Canada)

Tidal creeks in large coastal deltas can be important habitat for fish but are often highly modified by human activities. Connectivity between tributary creeks and mainstem channels is often constrained by structures such as dikes and floodgates, designed to protect urban and agricultural areas from flooding. While they play important roles in flood mitigation, floodgates can diminish habitat quality and block fish from accessing tidal creeks. It is likely that floodgates differ in their operations and may consequently open for different amounts of time; however, floodgate operations and their effects are not well quantified. We asked the question: how does the mechanical functioning of these floodgates affect fish communities in tidal creeks? We used time-lapse cameras and quantified the timing of gate openings for 22 tributaries of the Lower Fraser River in British Columbia, Canada, and related these operational data to differences in fish communities above and below floodgates. Floodgate operations varied substantially, with some floodgates opening daily while others opened less than 20% of the day, on average. Sites with floodgates that seldom opened were associated with greater differences in fish communities and with reduced upstream native species richness by about one species on average. Where floodgates opened infrequently, we also found lower upstream dissolved oxygen concentrations than at sites where floodgates opened for longer periods of time. Thus, floodgate operations can influence fish communities as well as water quality. These data indicate a large scope for improving floodgate operations for connectivity.     

The effects of visual realism,spatial abilities,and competition on performance in map-based route learning in men

We report on how visual realism might influence map-based route learning performance in a controlled laboratory experiment with 104 male participants in a competitive context. Using animations of a dot moving through routes of interest, we find that participants recall the routes more accurately with abstract road maps than with more realistic satellite maps. We also find that, irrespective of visual realism, participants with higher spatial abilities (high-spatial participants) are more accurate in memorizing map-based routes than participants with lower spatial abilities (low-spatial participants). On the other hand, added visual realism limits high-spatial participants in their route recall speed, while it seems not to influence the recall speed of low-spatial participants. Competition affects participants’ overall confidence positively, but does not affect their route recall performance neither in terms of accuracy nor speed. With this study, we provide further empirical evidence demonstrating that it is important to choose the appropriate map type considering task characteristics and spatial abilities. While satellite maps might be perceived as more fun to use, or visually more attractive than road maps, they also require more cognitive resources for many map-based tasks, which is true even for high-spatial users.     

Causes and consequences of long-term groundwater overabstraction in Jordan

Hydrogeology Journal - In 2017, a comprehensive review of groundwater resources in Jordan was carried out for the first time since 1995. The change in groundwater levels between 1995 and 2017 was...     

A Long Way to Go: Collective Paths to Racial Justice in Geography

Despite decades of recognition and worry about diversity, our discipline remains persistently white. That is, it is dominated by white bodies and it continues to conform to norms, practices, and ideologies of whiteness. This is a loss. At best, it limits the possibilities and impact of our work as geographers. At worst, it perpetuates harmful exclusions in our discipline: its working environments, its institutions, and its knowledge production. This remains deeply concerning for many geographers, and there has been important research, commentary, and institutional activity over the years. Yet, research shows us that little meaningful progress has been made. We know that mentoring is one vital part of the journey toward change. As such, we reflect here on our experience developing a research collective built on a transformative mentoring practice. We outline the key challenges, strategies, and tentative successes of the collective in supporting women of color undergraduate, graduate, and faculty geographers, arguing that such feminist formations are a vital part of the path to intellectual racial justice in our field. Key Words: diversity, feminist geography, higher education, mentoring, race.