22 research outputs found
The WAIS Divide Deep Ice Core WD2014 Chronology â Part 2: Annual-Layer Counting (0â31âŻkaâŻBP)
We present the WD2014 chronology for the upper part (0â2850âŻm; 31.2âŻkaâŻBP) of the West Antarctic Ice Sheet (WAIS) Divide (WD) ice core. The chronology is based on counting of annual layers observed in the chemical, dust and electrical conductivity records. These layers are caused by seasonal changes in the source, transport, and deposition of aerosols. The measurements were interpreted manually and with the aid of two automated methods. We validated the chronology by comparing to two high-accuracy, absolutely dated chronologies. For the Holocene, the cosmogenic isotope records of Be from WAIS Divide and C for IntCal13 demonstrated that WD2014 was consistently accurate to better than 0.5 % of the age. For the glacial period, comparisons to the Hulu Cave chronology demonstrated that WD2014 had an accuracy of better than 1 % of the age at three abrupt climate change events between 27 and 31 ka. WD2014 has consistently younger ages than Greenland ice core chronologies during most of the Holocene. For the Younger DryasâPreboreal transition (11.595 ka; 24 years younger) and the BĂžllingâAllerĂžd Warming (14.621 ka; 7 years younger), WD2014 ages are within the combined uncertainties of the timescales. Given its high accuracy, WD2014 can become a reference chronology for the Southern Hemisphere, with synchronization to other chronologies feasible using high-quality proxies of volcanism, solar activity, atmospheric mineral dust, and atmospheric methane concentrations
An 83 000-year-old ice core from Roosevelt Island, Ross Sea, Antarctica
In 2013 an ice core was recovered from Roosevelt Island, an ice dome between two submarine troughs carved by paleo-ice-streams in the Ross Sea, Antarctica. The ice core is part of the Roosevelt Island Climate Evolution (RICE) project and provides new information about the past configuration of the West Antarctic Ice Sheet (WAIS) and its retreat during the last deglaciation. In this work we present the RICE17 chronology, which establishes the depthâage relationship for the top 754âm of the 763âm core. RICE17 is a composite chronology combining annual layer interpretations for 0â343âm (Winstrup et al., 2019) with new estimates for gas and ice ages based on synchronization of CH4 and ÎŽ18Oatm records to corresponding records from the WAIS Divide ice core and by modeling of the gas ageâice age difference.
Novel aspects of this work include the following: (1) an automated algorithm for multiproxy stratigraphic synchronization of high-resolution gas records; (2) synchronization using centennial-scale variations in methane for pre-anthropogenic time periods (60â720âm, 1971âCE to 30âka), a strategy applicable for future ice cores; and (3) the observation of a continuous climate record back to âŒ65âka providing evidence that the Roosevelt Island Ice Dome was a constant feature throughout the last glacial period
Mass Stranding of Marine Birds Caused by a Surfactant-Producing Red Tide
In November-December 2007 a widespread seabird mortality event occurred in Monterey Bay, California, USA, coincident with a massive red tide caused by the dinoflagellate Akashiwo sanguinea. Affected birds had a slimy yellow-green material on their feathers, which were saturated with water, and they were severely hypothermic. We determined that foam containing surfactant-like proteins, derived from organic matter of the red tide, coated their feathers and neutralized natural water repellency and insulation. No evidence of exposure to petroleum or other oils or biotoxins were found. This is the first documented case of its kind, but previous similar events may have gone undetected. The frequency and amplitude of red tides have increased in Monterey Bay since 2004, suggesting that impacts on wintering marine birds may continue or increase
Seasonal temperatures in West Antarctica during the Holocene
The recovery of long-term climate proxy records with seasonal resolution is rare because of natural smoothing processes, discontinuities and limitations in measurement resolution. Yet insolation forcing, a primary driver of multimillennial-scale climate change, acts through seasonal variations with direct impacts on seasonal climate1. Whether the sensitivity of seasonal climate to insolation matches theoretical predictions has not been assessed over long timescales. Here, we analyse a continuous record of water-isotope ratios from the West Antarctic Ice Sheet Divide ice core to reveal summer and winter temperature changes through the last 11,000âyears. Summer temperatures in West Antarctica increased through the early-to-mid-Holocene, reached a peak 4,100âyears ago and then decreased to the present. Climate model simulations show that these variations primarily reflect changes in maximum summer insolation, confirming the general connection between seasonal insolation and warming and demonstrating the importance of insolation intensity rather than seasonally integrated insolation or season duration2,3. Winter temperatures varied less overall, consistent with predictions from insolation forcing, but also fluctuated in the early Holocene, probably owing to changes in meridional heat transport. The magnitudes of summer and winter temperature changes constrain the lowering of the West Antarctic Ice Sheet surface since the early Holocene to less than 162âm and probably less than 58âm, consistent with geological constraints elsewhere in West Antarctica4-7
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The WAIS Divide deep ice core WD2014 chronology - Part 2: Annual-layer counting (0-31 ka BP)
We present the WD2014 chronology for the upper part (0â2850 m; 31.2 ka BP) of the West Antarctic Ice Sheet (WAIS) Divide (WD) ice core. The chronology is based on counting of annual layers observed in the chemical, dust and electrical conductivity records. These layers are caused by seasonal changes in the source, transport, and deposition of aerosols. The measurements were interpreted manually and with the aid of two automated methods. We validated the chronology by comparing to two high-accuracy, absolutely dated chronologies. For the Holocene, the cosmogenic isotope records of Âčâ°Be from WAIS Divide and ÂčâŽC for IntCal13 demonstrated that WD2014 was consistently accurate to better than 0.5% of the age. For the glacial period, comparisons to the Hulu Cave chronology demonstrated that WD2014 had an accuracy of better than 1% of the age at three abrupt climate change events between 27 and 31 ka. WD2014 has consistently younger ages than Greenland ice core chronologies during most of the Holocene. For the Younger DryasâPreboreal transition (11.595 ka; 24 years younger) and the BĂžllingâAllerĂžd Warming (14.621 ka; 7 years younger), WD2014 ages are within the combined uncertainties of the timescales. Given its high accuracy, WD2014 can become a reference chronology for the Southern Hemisphere, with synchronization to other chronologies feasible using high-quality proxies of volcanism, solar activity, atmospheric mineral dust, and atmospheric methane concentrations
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Precise interpolar phasing of abrupt climate change during the last ice age
The last glacial period exhibited abrupt DansgaardâOeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archivesÂč. Ice cores show that Antarctica cooled during the warm phases of the Greenland DansgaardâOeschger cycle and vice versa[superscript 2,3], suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw[superscript 4â6]. Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events[superscript 7â9]. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision[superscript 2,3,10]. Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2Ï) for DansgaardâOeschger events, including the BĂžlling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of DansgaardâOeschger dynamics
Cross Adaptation - Heat and Cold Adaptation to Improve Physiological and Cellular Responses to Hypoxia
To prepare for extremes of heat, cold or low partial pressures of O2, humans can undertake a period of acclimation or acclimatization to induce environment specific adaptations e.g. heat acclimation (HA), cold acclimation (CA), or altitude training. Whilst these strategies are effective, they are not always feasible, due to logistical impracticalities. Cross adaptation is a term used to describe the phenomenon whereby alternative environmental interventions e.g. HA, or CA, may be a beneficial alternative to altitude interventions, providing physiological stress and inducing adaptations observable at altitude. HA can attenuate physiological strain at rest and during moderate intensity exercise at altitude via adaptations allied to improved oxygen delivery to metabolically active tissue, likely following increases in plasma volume and reductions in body temperature. CA appears to improve physiological responses to altitude by attenuating the autonomic response to altitude. While no cross acclimation-derived exercise performance/capacity data have been measured following CA, post-HA improvements in performance underpinned by aerobic metabolism, and therefore dependent on oxygen delivery at altitude, are likely. At a cellular level, heat shock protein responses to altitude are attenuated by prior HA suggesting that an attenuation of the cellular stress response and therefore a reduced disruption to homeostasis at altitude has occurred. This process is known as cross tolerance. The effects of CA on markers of cross tolerance is an area requiring further investigation. Because much of the evidence relating to cross adaptation to altitude has examined the benefits at moderate to high altitudes, future research examining responses at lower altitudes should be conducted given that these environments are more frequently visited by athletes and workers. Mechanistic work to identify the specific physiological and cellular pathways responsible for cross adaptation between heat and altitude, and between cold and altitude, is warranted, as is exploration of benefits across different populations and physical activity profiles
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Gas isotope thermometry in the South Pole and Dome Fuji ice cores provides evidence for seasonal rectification of ice core gas records
Abstract. Gas isotope thermometry using the isotopes of molecular nitrogen and argon
has been used extensively to reconstruct past surface temperature change
from Greenland ice cores. The gas isotope ratios ÎŽ15N and
ÎŽ40Ar in the ice core are each set by the amount of
gravitational and thermal fractionation in the firn. The gravitational
component of fractionation is proportional to the firn thickness, and the
thermal component is proportional to the temperature difference between the
top and bottom of the firn column, which can be related to surface
temperature change. Compared to Greenland, Antarctic climate change is
typically more gradual and smaller in magnitude, which results in smaller
thermal fractionation signals that are harder to detect. This has hampered
application of gas isotope thermometry to Antarctic ice cores. Here, we present an analytical method for measuring ÎŽ15N and
ÎŽ40Ar with a precision of 0.002ââ° per atomic
mass unit, a two-fold improvement on previous work. This allows us to
reconstruct changes in firn thickness and temperature difference at the South
Pole between 30 and 5âkyrâBP. We find that variability in firn thickness is
controlled in part by changes in snow accumulation rate, which is, in turn,
influenced strongly by the along-flowline topography upstream of the ice
core site. Variability in our firn temperature difference record cannot be
explained by annual-mean processes. We therefore propose that the ice core
gas isotopes contain a seasonal bias due to rectification of seasonal
signals in the upper firn. The strength of the rectification also appears to
be linked to fluctuations in the upstream topography. As further evidence
for the existence of rectification, we present new data from the Dome Fuji
ice core that are also consistent with a seasonal bias throughout the
Holocene. Our findings have important implications for the interpretation of ice core
gas records. For example, we show that the effects of upstream topography on
ice core records can be significant at flank sites like the South Pole â they
are responsible for some of the largest signals in our record. Presumably
upstream signals impact other flank-flow ice cores such as EDML, Vostok, and
EGRIP similarly. Additionally, future work is required to confirm the
existence of seasonal rectification in polar firn, to determine how spatially
and temporally widespread rectifier effects are, and to incorporate the
relevant physics into firn air models