Holocene climate recorded by magnetic properties of lake sediments in the Northern Rocky Mountains, USA

The Holocene ◽  
2019 ◽  
Vol 30 (3) ◽  
pp. 479-484
Author(s):  
Daniel P Maxbauer ◽  
Mark D Shapley ◽  
Christoph E Geiss ◽  
Emi Ito
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Rocky Mountains ◽  
Future Research ◽  
Magnetic Minerals ◽  
Holocene Climate ◽  
Northern Rocky Mountains ◽  
The North ◽  
Lake Bottom ◽  
Northern Rockies

We present two hypotheses regarding the evolution of Holocene climate in the Northern Rocky Mountains that stem from a previously unpublished environmental magnetic record from Jones Lake, Montana. First, we link two distinct intervals of fining magnetic grain size (documented by an increasing ratio of anhysteretic to isothermal remanent magnetization) to the authigenic production of magnetic minerals in Jones Lake bottom waters. We propose that authigenesis in Jones Lake is limited by rates of groundwater recharge and ultimately regional hydroclimate. Second, at ~8.3 ka, magnetic grain size increases sharply, accompanied by a drop in concentration of magnetic minerals, suggesting a rapid termination of magnetic mineral authigenesis that is coeval with widespread effects of the 8.2 ka event in the North Atlantic. This association suggests a hydroclimatic response to the 8.2 ka event in the Northern Rockies that to our knowledge is not well documented. These preliminary hypotheses present compelling new ideas that we hope will both highlight the sensitivity of magnetic properties to record climate variability and attract more work by future research into aridity, hydrochemical response, and climate dynamics in the Northern Rockies.

Environmental magnetism study of Lake Cadagno, Switzerland

2021 ◽  
Author(s):  
Artin Ali ◽  
Andrea Biedermann ◽  
Jasmine Berg ◽  
Mark Lever ◽  
Hendrik Vogel
Keyword(s):  
Grain Size ◽  
Sedimentary Environment ◽  
Environmental Magnetism ◽  
Late Glacial ◽  
Magnetic Minerals ◽  
Climate Conditions ◽  
Glacial Sediments ◽  
Depth Profiles ◽  
Magnetic Carriers ◽  
Lake Bottom

<p>Climate affects the mineralogy and grain size of sediments deposited in lakes. These properties are reflected in the sediment magnetic properties and can be characterized using magnetic methods. As part of the Cadagno-Project, which recovered several gravity and piston cores spanning the entire lake history from the deglacial to the present from the deepest part of permanently stratified Lake Cadagno, which is due to its peculiar water column chemistry considered an early Earth ocean analogue, our study aims to define changes in climate conditions during sedimentation. Here, we present a rock magnetic dataset (low-field magnetic susceptibility and its temperature dependence, anhysteretic and isothermal remanent magnetization (ARM, IRM), acquired in various fields, AF demagnetization, and hysteresis loops) that helps characterize the concentration, mineralogy, and grain size of magnetic carriers, and their variability with depth. Susceptibility, ARM, and IRM were measured on core sediments down to a depth of 886 cm below the lake bottom, providing a high-resolution record of the sedimentary environment of Lake Cadagno over the last 11,000 years. In addition to these depth profiles, detailed rock magnetic experiments were conducted at specific depths. The cores consist of pelagic sediments, flood turbidites, and late glacial sediments. In order to determine the characteristics of the background sedimentation, only turbidite-free intervals were included in this study. The depth profiles of susceptibility, ARM and IRM have approximately similar variations with depth. They show distinct peaks at the upper parts of the pelagic sediments (156-158 cm below the lake bottom,   ̴1280-1320 cal. Yr Bp) and of the late glacial sediments (826-844 cm below the lake bottom), which can be interpreted as increased concentration of ferromagnetic minerals or as a change in the magnetic mineralogy, in addition to decreasing trend in the background. Several intervals within the pelagic sediments are dominated by low-coercivity minerals (<10 mT), while higher coercivity grains (10–100 mT) contribute significantly at (150-170, 418-448 and 719-735 cm below the lake bottom). Magnetic grain size was analyzed using a Day plot, and shows that single domain magnetite dominates at (844 cm) below the lake bottom, indicating the presence of magnetotactic bacteria, which are believed to dwell mainly in the oxic–anoxic interface where chemical gradients are high. These results provide important constraints on the environmental conditions and climate change recorded by the magnetic minerals in Lake Cadagno.</p>

scholarly journals Magnetic Properties of a Holocene Sediment Core from the Yeongsan Estuary, Southwest Korea: Implications for Diagenetic Effects and Availability as Paleoenvironmental Proxies

2021 ◽  
Vol 9 ◽  
Author(s):  
Hyeon–Seon Ahn ◽  
Jaesoo Lim ◽  
Sung Won Kim
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Magnetic Susceptibility ◽  
South Korea ◽  
Size Distribution ◽  
Sea Level ◽  
West Coast ◽  
Magnetic Minerals ◽  
The West ◽  
Saturation Moment

The sensitivity of magnetic properties, which characterize the mineralogy, concentration, and grain size distribution of magnetic minerals, to environmental processes may provide useful information on paleoenvironmental changes in estuarine environments. Magnetic property studies of estuaries are less common than other environments and, due to the west coast of South Korea having an abundance of estuaries, it provides a good place to study these processes. In this study, we analyzed a variety of magnetic properties based on magnetic susceptibility, hysteresis parameters, progressive acquisition of isothermal remanent magnetization and first-order reversal curve data from a Holocene muddy sediment core recovered from the Yeongsan Estuary on the west coast of South Korea. We examined diagenetic effects on magnetic properties and tested their availability as proxies of paleoenvironmental change. The presence of generally low magnetic susceptibility, ubiquitous greigite-like authigenic magnetic component, and very fine magnetic particle occurrence suggested that the analyzed sediments had undergone considerable early diagenetic alteration. Electron microscopic observations of magnetic minerals support this suggestion. Our results confirm that the use of initial bulk susceptibility as a stand-alone environmental change proxy is not recommended unless it is supported by additional magnetic analyses. We recognized the existence of ferromagnetic-based variabilities related to something besides the adverse diagenetic effects, and have examined possible relationships with sea-level and major climate changes during the Holocene. The most remarkable finding of this study is the two distinct intervals with high values in magnetic coercivity (Bc), coercivity of remanence (Bcr), and ratio of remanent saturation moment to saturation moment (Mrs/Ms) that were well coincident with the respective abrupt decelerations in the rate of sea-level rise occurred at around 8.2 and 7 thousand years ago. It is then inferred that such condition with abrupt drop in sea-level rise rate would be favorable for the abrupt modification of grain size distribution toward more single-domain-like content. We modestly propose consideration of the Bc, Bcr, and Mrs/Ms variability as a potential indicator for the initiation/occurrence of sea-level stillstand/slowstand or highstand during the Holocence, at least at estuarine environments in and around the studied area.

scholarly journals High elevation ice patch documents Holocene climate variability in the northern Rocky Mountains

2021 ◽  
Vol 3 ◽  
pp. 100021
Author(s):  
Nathan J. Chellman ◽  
Gregory T. Pederson ◽  
Craig M. Lee ◽  
David B. McWethy ◽  
Kathryn Puseman ◽  
...  
Keyword(s):  
Climate Variability ◽  
Rocky Mountains ◽  
High Elevation ◽  
Holocene Climate ◽  
Northern Rocky Mountains

Postglacial record of diatom assemblage changes related to climate in an alpine lake in the northern Rocky Mountains, Canada

2005 ◽  
Vol 83 (8) ◽  
pp. 968-982 ◽  
Author(s):  
Tammy L Karst-Riddoch ◽  
Michael FJ Pisaric ◽  
Donald K Youngblut ◽  
John P Smol
Keyword(s):  
Rocky Mountains ◽  
Fire Frequency ◽  
Alpine Lake ◽  
Alpine Tundra ◽  
Benthic Habitat ◽  
Diatom Assemblages ◽  
Holocene Climate ◽  
Northern Rocky Mountains ◽  
Vegetation Shifts ◽  
Diatom Communities

We relate changes in diatom assemblages to Holocene climate since ca. 10 300 cal. years BP at a small (4 ha), alkaline, alpine tundra lake in the Rocky Mountains of northeast British Columbia. A complex of small benthic Fragilaria-type taxa generally dominated the fossil diatom communities reflecting shallow, alkaline, and likely low light conditions resulting from minerogenic turbidity or extensive ice cover throughout the Holocene. Shifts in diatom assemblages occurred with changes in local vegetation, inferred from pollen and stomate records, and shifts in charcoal-inferred fire frequency (e.g., lowering of tree line and reduced fire frequency (approx. 7500 cal. years BP) and establishment of modern alpine tundra (approx. 3500 cal. years BP). Importantly, striking changes in diatom communities (e.g., during the mid-Holocene (approx. 5500 to approx. 3500 cal. years BP) and Medieval Warm Period (approx. AD 800 to approx. AD 1250)) occurred without evidence of vegetation shifts. During these times, diverse periphytic diatoms dominated suggesting improved benthic habitat availability with longer growing seasons and probably reduced alkalinity and turbidity with warmer- and wetter-than-present climates. Diatom analysis from this alpine lake provides a sensitive record of climate-related limnological responses, but also refines our previous understanding of Holocene climate changes in the northern Rocky Mountains inferred from terrestrial-based paleoecological records.Key words: alkalinity, alpine lakes, climate change, diatoms, Holocene, paleolimnology.

A structural interpretation across part of the northern Rocky Mountains, British Columbia, Canada

1979 ◽  
Vol 16 (6) ◽  
pp. 1228-1241 ◽  
Author(s):  
Robert I. Thompson
Keyword(s):  
British Columbia ◽  
Rocky Mountains ◽  
Lateral Displacement ◽  
Rocky Mountain ◽  
Thrust Faults ◽  
Northern Rocky Mountains ◽  
Eastern Margin ◽  
The North ◽  
Structural Style ◽  
Mountain Front

The northern Canadian Rocky Mountains, as exemplified by the Halfway River map-area (94B) in British Columbia, consists of a rugged and mountainous structurally complex Foothills subprovince of large amplitude box and chevron-style folds in rocks of late Paleozoic and Mesozoic age, and a structurally diverse Rocky Mountain subprovince with open folds and apparently inconspicuous thrust faults in upper Precambrian to upper Paleozoic rocks; separating them is a narrow topographically subdued and heavily vegetated 'transition interval' comprising more penetratively folded and faulted shales and thin-bedded carbonate rocks of late Devonian and Mississippian age.Flat thrust faults, with displacements in the order of 10 km, which occur under the eastern margin of the Rocky Mountain subprovince (mountain front) extend across the 'transition interval' and beneath the western margin of the Foothills subprovince. These faults terminate within a décollement along the Devonian and Mississippian Besa River shale, as the displacement on them is transformed into disharmonic kink-type box and chevron folds in overlying units and into tectonic thickening within the Besa River shale. Because most of the major thrust faults along the Rocky Mountains are 'blind' and cannot be traced to surface exposures, one is left with the erroneous impression that very little lateral displacement (foreshortening) has occurred in the northern Canadian Rocky Mountains.The basic change from a well organized thrust-fault terrane in the southern Rockies to a more diverse fold terrane with few large mappable thrusts in the north is consistent with changes in the stratigraphic character of the rock prism that was deformed: the proportion of thick incompetent shale units increases northward, and major lateral carbonate to shale facies transitions traverse the eastern margin of the Rocky Mountain subprovince.Despite the differences in structural style from south to north, strain patterns within the northern Rocky Mountains are consistent with the lateral eastward movement of a detached prism of sedimentary rocks, and support the basic tenets of thin-skinned tectonics.

scholarly journals A list of bees from three locations in the Northern Rockies Ecoregion (NRE) of western Montana

2018 ◽  
Vol 6 ◽  
Author(s):  
Elizabeth Reese ◽  
Laura Burkle ◽  
Casey Delphia ◽  
Terry Griswold
Keyword(s):  
Rocky Mountains ◽  
Western Montana ◽  
Wild Bees ◽  
Northern Rocky Mountains ◽  
Basic Understanding ◽  
Northern Rockies

Wild bees that were collected in conjunction with a larger study are presented as a checklist of species for the Northern Rockies Ecoregion of Montana, USA. Over the course of four field seasons (2013-2016), 281 species and morphospecies in 32 genera and five families were collected using insect nets, and identified. This paper addresses the distinct lack of studies monitoring bee species in Montana and contributes to a basic understanding of fauna in the northern Rocky Mountains.With this study, the number of known bee species in Montana increases by at least six species, from 366 (Kuhlman and Burrows 2017) to 372. Though literature was not reviewed for all the species on this checklist, published records in Montana revealed no listings forAndrenasaccataViereck;Anthidiellumnotatumrobertsoni(Cockerell);Ashmeadiellameliloti(Cockerell);Ashmeadiellapronitens(Cockerell);ColleteslutzilutziTimberlake; andDioxysproductus(Cresson).

Obliquity pacing of Antarctic glaciations during the Quaternary

2020 ◽  
Author(s):  
Christian Ohneiser ◽  
Catherine Beltran ◽  
Christina Hulbe ◽  
Chris Moy ◽  
Christina Riesselman ◽  
...  
Keyword(s):  
Grain Size ◽  
Oxygen Isotope ◽  
Ice Core ◽  
Size Fraction ◽  
Data Series ◽  
Magnetic Minerals ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Xrf Core Scanner

<p>Obliquity pacing of Antarctic glaciations during the Quaternary</p><p>The frequency of Antarctic glaciations during the Quaternary are not well understood. Benthic oxygen isotope records provide evidence for eccentricity paced global ice volume changes since c. 800 000 years and the ice core records (such as EPICA) also appear to have 100 000 year cycles over the last 800 000 years. However, the benthic oxygen isotope records are a global average – not an Antarctic record. Quaternary, sedimentary records proximal to the ice margin (such as the ANDRILL AND-1B record) are needed to understand better the recent glacial history of Antarctica. </p><p>Here we present results from the 6.21 m long, NBP03-01A-20PCA sedimentary record which was recovered from the outer continental margin of the Ross Embayment.</p><p>Sediments comprise mud with numerous clasts and paleomagnetic analyses revealed magnetic reversals at 4.21 m, 5.74 m, and 5.85 m depth. These reversals are correlated with C1n-C1r.1r-C1r.1n-C1r.2r geomagnetic reversals which have corresponding ages of 773 ka, 990 ka, and 1070 ka. </p><p>Time series analysis of continuous Anhysteretic Remanent Magnetisation (ARM) data, which are controlled primarily by the concentration of magnetic minerals, revealed strong obliquity paced cycles between c. 800 ka and 350 ka. The presence of obliquity cycles prompted us to carry out core scanning XRF and grain size analyses. The archive half was scanned in a itrax XRF core scanner at the Marine and Geology Repository at Oregon State University and high density grain size analyses were conducted at the University of Otago. </p><p>We identified obliquity paced cycles in the titanium elemental data over the same period which we suggest represent variations in the terrigenous material in the core. Weaker obliquity cycles are also present in the >2mm grain size fraction which we suggest is controlled by the proximity of the ice shelf front. </p><p>We suggest that the presence of obliquity paced cycles in our data series indicate that the Ross Ice Shelf calving line advance and retreat cycles were paced with obliquity until at least 350 ka and that the mid-Pleistocene transition occurred later in the Southern Hemisphere than in the North. </p>

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