Climatic Oscillations 10,000–155,000 yr B.P. at Owens Lake, California Reflected in Glacial Rock Flour Abundance and Lake Salinity in Core OL-92

Chemical analyses of the acid-soluble and clay-size fractions of sediment samples (1500-yr resolution) reveal oscillations of lake salinity and of glacial advances in core OL-92 back to 155,000 yr B.P. Relatively saline conditions are indicated by the abundance of carbonate and smectite (both pedogenic and authigenic), reflected by Ca, Sr, and Mg in the acid-soluble suite, and by Cs₂O, excess MgO, and LOI (loss on ignition) in the clay-size fraction. Rock flour produced during glacial advances is represented by the abundance of detrital plagioclase and biotite in the clay-size fraction, the ratio of which remains essentially constant over the entire time span. These phases are quantitatively represented by Na₂O, TiO₂, Ba, and Mn in the clay fraction. The rock-flour record indicates two major ice-advances during the penultimate glacial cycle corresponding to marine isotope stage (MIS) 6, no major advances during the last interglaciation (entire MIS 5), and three major advances during the last glacial cycle (MIS 2, 3, and 4). The ages of the latter three correspond rather well to³⁶Cl dates reported for Sierra Nevada moraines. The onset of the last interglaciation is shown by abrupt increases in authigenic CaCO₃and an abrupt decrease in rock flour, at about 118,000 yr B.P. according to our time scale. In contrast, the boundary appears to be gradual in the δ¹⁸O record in which the change from light to heavy values begins at about 140,000 yrs B.P. The exact position of the termination, therefore, may be proxy-dependent. Conditions of high carbonate and low rock flour prevailed during the entire period from 118,000 yr B.P. until the glacial advance at 53,000 yr B.P. signaled the end of this long interglaciation.     

Metropolitan land-use patterns by economic function: a spatial analysis of firm headquarters and branch office locations in Australian cities

This paper develops a comparative means by which to understand metropolitan spatial structure through the dynamics of economic activities. Clustering and suburbanization have been key processes within the contemporary urban landscape, but few scholarly accounts have systematically merged the two to explain the geographies of economic activity. Using firm location as a variable to discern sector- and industry-based locational requirements, we explore land-use and economic activity in Australia’s five largest metropolitan areas. Drawing upon the respective headquarters and branch office locations of a set of publically traded firms, we seek to establish general spatial patterns across Australian cities using two proxy measures for clustering and suburbanization, being well-established drivers of firm locational choice. Despite the complexity that post-industrial and suburbanizing processes add to metropolitan land-use patterns, we contend that certain patterns exist that can be generalized from one context to another across urban space, and that certain emerging trends such as the development of CBD-fringe precincts merit greater attention.     

Maada’oonidiwag gete-dibaajimowen (“sharing old stories”): reflections on a place-based reparatory research partnership in Nbisiing Anishinaabeg Territory

In this paper, we reflect on an emerging community-based partnership rooted in place-based reparative research. Braiding knowledges (Atalay, 2012) from Nbisiing Anishinaabeg communities, northern Ontario universities, and multi-scalar museums, the partnership focuses on repatriation, reparative environmental histories, and action-based research in the context of settler colonialism and climate change. We reflect on ongoing projects that attempt to put Anishinaabe gikendaasowin (knowledge) into action alongside historical geographical research. We discuss how the partnership resonates with community geography values of relationship, collaboration, equity, and reciprocity, and urge non-Indigenous geographers to acknowledge how Indigenous knowledges and approaches have shaped these ideas long before geography became a discipline. We contend that historical geographers have a deeper role to play in community geography scholarship, citing examples of two projects related to (1) repatriation of Anishinaabeg cultural heritage and (2) storymapping through historical Geographic Information Systems (HGIS). However, we argue, geographers must continue to acknowledge their own positionality in a discipline that was built through settler colonial violence and knowledge production. Finally, we reflect on the role of academic institutions in facilitating First Nation-university-museum partnerships through access to funding, space, and databases, while addressing the challenges of relying on institutional support for reparatory and decolonizing projects.

     

Expanded response-surfaces: a new method to reconstruct paleoclimates from fossil pollen assemblages that lack modern analogues

Pollen-based paleoclimatic interpretations of late-glacial to early Holocene climates (17–9 ka) in Midwestern North America are hampered by samples that lack modern analogues. Unresolved questions include the magnitude and direction of temperature seasonality (i.e. were these climates more or less seasonal than present) and the temporal changes in precipitation. Central to the no-analogue problem is the truncation of modern pollen-climate relationships for abundant late-glacial taxa such as Fraxinus. Here we present a new method called the expanded response-surface (ERS) method, developed to reconstruct climates from no-analogue pollen assemblages and applied to a high-resolution late-glacial pollen record from Crystal Lake, Illinois to test hypotheses about late-glacial climates. The key assumptions central to the ERS method are: (1) plant species and pollen abundances follow symmetrical unimodal distributions along climatic gradients, (2) taxa with truncated distributions in modern climate space occupy a subset of their fundamental niche, and (3) expansion of truncated distributions by mirroring around the distributional mode recovers the portion of the fundamental niche not realized in the modern climate space. With the ERS method, we expanded modern pollen-climate relationships by mirroring pollen abundances for each taxon around a mode defined with respect to four climate axes (mean winter temperature, mean summer temperature, mean winter precipitation, and mean summer precipitation). The ERS method reconstructed past temperatures and precipitation during the height of no-analogue conditions (14 160–12 370 cal yr BP) for 37% of the Crystal Lake samples where techniques that employed only modern observational data found matches for only 13% of the fossil samples. The total climate space of the expanded taxa set allowed analogue matches under more seasonal-than-present climates with higher-than-present precipitation. The ERS climate reconstructions for the height of no-analogue conditions indicated cooler-than-present summer and winter temperatures, similar-to-present seasonal range in temperatures, higher-than-present winter precipitation, and similar-to-present summer precipitation. These results thus suggest that high moisture availability helped drive the formation of the Midwestern no-analogue communities with high Fraxinus nigra abundances, but do not show higher-than-present temperature seasonality notwithstanding the higher-than-present insolation seasonality at this time. During the no-analogue late-glacial interval, Picea mariana, F. nigra, and Larix stands probably grew on low-lying, poorly drained soils in the Crystal Lake region; whereas Abies, Picea glauca, Quercus, and Ostrya/Carpinus grew on upland positions with better soil drainage.     

Particle sedimentation patterns in the eastern Fram Strait during 2000–2005: Results from the Arctic long-term observatory HAUSGARTEN

Since 2000 long-term measurements of vertical particle flux have been performed with moored sediment traps at the long-term observatory HAUSGARTEN in the eastern Fram Strait (79°N/4°E). The study area, which is seasonally covered with ice, is located in the confluence zone of the northward flowing warm saline Atlantic water with cold, low salinity water masses of Arctic origin. Current projections suggest that this area is particularly vulnerable to global warming. Total matter fluxes and components thereof (carbonate, particulate organic carbon and nitrogen, biogenic silica, biomarkers) revealed a bimodal seasonal pattern showing elevated sedimentation rates during May/June and August/September. Annual total matter flux (dry weight, DW) at ～300 m depth varied between 13 and 32 g m^?2 a^?1 during 2000 and 2005. Of this total flux 6–13% was due to CaCO₃, 4–21% to refractory particulate organic carbon (POC), and 3–8% to biogenic particulate silica (bPSi). The annual flux of all biogenic components together was almost constant during the period studied (8.5–8.8 g m^?2 a^?1), although this varied from 27% to 67% of the total annual flux. The fraction was lowest in a year characterized by the longest duration of ice coverage (91 and 70 days for the calendar year and summer season, May–September, respectively). Biomarker analyses revealed that organic matter originating from marine sources was present in excess of terrigenious material in the sedimented matter throughout most of the study period. Fluxes of recognizable phyto- and protozooplankton cells amounted up to 60×10⁶ m^?2 d^?1. Diatoms and coccolithophorids were the most abundant organisms. Diatoms, mainly pennate species, dominated during the first years of the investigation. A shift in the composition occurred during the last year when numbers of diatoms declined considerably, leading to a dominance of coccolithoporids. This was also reflected in a decrease in the sedimentation of bPSi. The sedimentation of biogenic matter, however, did not differ from the amount observed during the previous years. Among the larger organisms, pteropods at times contributed significantly to both the total matter and CaCO₃, fluxes.     

Modeling and simulating earthquake accelerograms using strong-motion data from the Istanbul, Turkey, region

In order to simulate earthquake ground motions for the Instanbul (Turkey) region, acceleration time series from western Turkey are modeled by transforming the series into a stationary one which can be described by an autoregressive moving-average (ARMA) process. The ARMA and other parameters used in the stationary transformation are related to physical parameters (e.g. magnitude, distance to epicenter, depth to hypocenter and duration) via a regression analysis. To create simulations for a given set of physical parameters, the modelling procedure is reversed.     

Wetter or colder during the Last Glacial Maximum? Revisiting the pluvial lake question in southwestern North America

Well-preserved shorelines in Estancia basin and a relatively simple hydrologic setting have prompted several inquiries into the basin's hydrologic balance for the purpose of estimating regional precipitation during the late Pleistocene. Estimates have ranged from 86% to 150% of modern, the disparity largely the result of assumptions about past temperatures. In this study, we use an array of models for surface-water runoff, groundwater flow, and lake energy balance to examine previously proposed scenarios for late Pleistocene climate. Constraints imposed by geologic evidence of past lake levels indicate that precipitation for the Last Glacial Maximum (LGM) may have doubled relative to modern values during brief episodes of colder and wetter climate and that annual runoff was as much as 15% of annual precipitation during these episodes.     

Sedimentologic and stratigraphic constraints on emplacement of the Star Kimberlite, east–central Saskatchewan

Diamond-bearing kimberlites in the Fort à la Corne region, east–central Saskatchewan, consist primarily of extra-crater pyroclastic deposits which are interstratified with Lower Cretaceous (Albian and Cenomanian) marine, marginal marine and continental sediments. Approximately 70 individual kimberlite occurrences have been documented. The Star Kimberlite, occurring at the southeastern end of the main Fort à la Corne trend, has been identified as being of economic interest, and is characterized by an excellent drill core database. Integration of multi-disciplinary data-sets has helped to refine and resolve models for emplacement of the Star Kimberlite. Detailed core logging has provided the foundation for sedimentological and volcanological studies and for construction of a regionally consistent stratigraphic and architectural framework for the kimberlite complex. Micropaleontologic and biostratigraphic analysis of selected sedimentary rocks, and U–Pb perovskite geochronology on kimberlite samples have been integrated to define periods of kimberlite emplacement. Radiometric age determination and micropaleontologic evidence support the hypothesis that multiple kimberlite eruptive phases occurred at Star. The oldest kimberlite in the Star body erupted during deposition of the predominantly continental strata of the lower Mannville Group (Cantuar Formation). Kimberlites within the Cantuar Formation include terrestrial airfall deposits as well as fluvially transported kimberlitic sandstone and conglomerate. Successive eruptive events occurred contemporaneous with deposition of the marginal marine upper Mannville Group (Pense Formation). Kimberlites within the Pense Formation consist primarily of terrestrial airfall deposits. Fine- to medium-grained cross-stratified kimberlitic (olivine-dominated) sandstone in this interval reflects reworking of airfall deposits during a regional marine transgression. The location of the source feeder vents of the Cantuar and Pense kimberlite deposits has not been identified. The youngest and volumetrically most significant eruptive events associated with the Star Kimberlite occur within the predominantly marine Lower Colorado Group (Joli Fou and Viking Formations). Kimberlite beds, which occur at several horizons within these units, consist of subaerial and marine fall deposits, the latter commonly exhibiting evidence of wave-reworking. Black shale-encased resedimented kimberlite beds, likely deposited as subaqueous debris flows and turbidites, are particularly common in the Lower Colorado Group. During its multi-eruptive history, the Star Kimberlite body is interpreted to have evolved from a feeder vent and overlying positive-relief tephra ring, into a tephra cone. Initial early Joli Fou volcanism resulted in formation of a feeder vent (200 m diameter) and tephra ring. Subsequent eruptions, dominated by subaerial deposits, partly infilled the crater and constructed a tephra cone. A late Joli Fou eruption formed a small (70 m diameter) feeder pipe slightly offset to the NW of the early Joli Fou feeder vent. Deposits from this event further infilled the crater, and were deposited on top of early Joli Fou kimberlite (proximal to the vent) and sediments of the Joli Fou Formation (distal to the vent). The shape of the tephra cone was modified during multiple marine transgression and regression cycles coeval with deposition of the Lower Colorado Group, resulting in wave-reworked kimberlite sand along the fringes of the cone and kimberlitic event deposits (tempestites, turbidites, debris flows) in more distal settings.