scholarly journals Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen station, Dronning Maud Land

2015 ◽  
Vol 11 (6) ◽  
pp. 5605-5649 ◽  
Author(s):  
T. Münch ◽  
S. Kipfstuhl ◽  
J. Freitag ◽  
H. Meyer ◽  
T. Laepple
Keyword(s):  
Isotope Composition ◽  
Ice Cores ◽  
Minor Role ◽  
Two Dimensional ◽  
Study Region ◽  
Climate Signal ◽  
Total Uncertainty ◽  
Climate Reconstructions ◽  
Dronning Maud Land ◽  
Isotopic Variations

Abstract. In low-accumulation regions, the reliability of δ18O-derived temperature signals from ice cores within the Holocene is unclear, primarily due to small Holocene climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen station, Dronning Maud Land, Antarctica. Analysing δ18O in two 50 m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the hundred-metre scale. Our results show a clear seasonal layering of the isotopic composition, consistent with the accumulation rate, as well as high lateral isotopic variability caused by local stratigraphic noise. Based on the horizontal and vertical structure of the isotopic variations, we derive a statistical model for the stratigraphic noise. Our model successfully explains the trench data and allows to determine an upper bound of the reliability of climate reconstructions from seasonal to inter-annual time scales, depending on the number and the spacing of the cores taken. Implications for our study region include that reliably detecting a warming trend (0.1 °C decade−1) in 50 years of data would require ∼10–50 replicate cores with a horizontal spacing of at least 10 m. More generally, our results suggest that in order to obtain high-resolution records of Holocene temperature change, fast measurements, thus allowing multiple cores, are more important than to minimise analytic uncertainty as the latter only plays a minor role in the total uncertainty.

scholarly journals Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land

2016 ◽  
Vol 12 (7) ◽  
pp. 1565-1581 ◽  
Author(s):  
Thomas Münch ◽  
Sepp Kipfstuhl ◽  
Johannes Freitag ◽  
Hanno Meyer ◽  
Thomas Laepple
Keyword(s):  
Isotope Composition ◽  
Regional Climate ◽  
Ice Cores ◽  
Noise Model ◽  
Two Dimensional ◽  
Study Region ◽  
Climate Signal ◽  
Climate Reconstructions ◽  
Dronning Maud Land ◽  
Isotopic Variations

Abstract. In low-accumulation regions, the reliability of δ18O-derived temperature signals from ice cores within the Holocene is unclear, primarily due to the small climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen Station, Dronning Maud Land, Antarctica. Analysing δ18O in two 50 m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the 100-metre scale. Our results show seasonal layering of the isotopic composition but also high horizontal isotopic variability caused by local stratigraphic noise. Based on the horizontal and vertical structure of the isotopic variations, we derive a statistical noise model which successfully explains the trench data. The model further allows one to determine an upper bound for the reliability of climate reconstructions conducted in our study region at seasonal to annual resolution, depending on the number and the spacing of the cores taken.

scholarly journals Variability of sea salts in ice and firn cores from Fimbul Ice Shelf, Dronning Maud Land, Antarctica

2018 ◽  
Vol 12 (5) ◽  
pp. 1681-1697 ◽  
Author(s):  
Carmen Paulina Vega ◽  
Elisabeth Isaksson ◽  
Elisabeth Schlosser ◽  
Dmitry Divine ◽  
Tõnu Martma ◽  
...  
Keyword(s):  
Sea Ice ◽  
Major Ions ◽  
Ice Cores ◽  
Precipitation Chemistry ◽  
Sea Salt ◽  
Ice Shelf ◽  
Study Region ◽  
Sea Salt Aerosol ◽  
Antarctic Sea Ice ◽  
Dronning Maud Land

Abstract. Major ions were analysed in firn and ice cores located at Fimbul Ice Shelf (FIS), Dronning Maud Land – DML, Antarctica. FIS is the largest ice shelf in the Haakon VII Sea, with an extent of approximately 36 500 km2. Three shallow firn cores (about 20 m deep) were retrieved in different ice rises, Kupol Ciolkovskogo (KC), Kupol Moskovskij (KM), and Blåskimen Island (BI), while a 100 m long core (S100) was drilled near the FIS edge. These sites are distributed over the entire FIS area so that they provide a variety of elevation (50–400 m a.s.l.) and distance (3–42 km) to the sea. Sea-salt species (mainly Na+ and Cl−) generally dominate the precipitation chemistry in the study region. We associate a significant sixfold increase in median sea-salt concentrations, observed in the S100 core after the 1950s, to an enhanced exposure of the S100 site to primary sea-salt aerosol due to a shorter distance from the S100 site to the ice front, and to enhanced sea-salt aerosol production from blowing salty snow over sea ice, most likely related to the calving of Trolltunga occurred during the 1960s. This increase in sea-salt concentrations is synchronous with a shift in non-sea-salt sulfate (nssSO42−) toward negative values, suggesting a possible contribution of fractionated aerosol to the sea-salt load in the S100 core most likely originating from salty snow found on sea ice. In contrast, there is no evidence of a significant contribution of fractionated sea salt to the ice-rises sites, where the signal would be most likely masked by the large inputs of biogenic sulfate estimated for these sites. In summary, these results suggest that the S100 core contains a sea-salt record dominated by the proximity of the site to the ocean, and processes of sea ice formation in the neighbouring waters. In contrast, the ice-rises firn cores register a larger-scale signal of atmospheric flow conditions and a less efficient transport of sea-salt aerosols to these sites. These findings are a contribution to the understanding of the mechanisms behind sea-salt aerosol production, transport and deposition at coastal Antarctic sites, and the improvement of the current Antarctic sea ice reconstructions based on sea-salt chemical proxies obtained from ice cores.

Correlated Millennial-Scale Changes in Surface Hydrography and Terrigenous Sediment Yield Inferred from Last-Glacial Marine Deposits off Northeastern Brazil

1998 ◽  
Vol 50 (2) ◽  
pp. 157-166 ◽  
Author(s):  
Helge W. Arz ◽  
Jürgen Pätzold ◽  
Gerold Wefer
Keyword(s):  
North Atlantic ◽  
Isotope Composition ◽  
Sediment Cores ◽  
Ice Cores ◽  
Northeastern Brazil ◽  
Salt Flux ◽  
Terrigenous Sediment ◽  
The North ◽  
North Brazil ◽  
The North Atlantic

The stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern Brazil. Stable oxygen isotope records of the planktonic foraminiferal species Globigerinoides sacculiferand Globigerinoides ruber(pink) reveal sub-Milankovitch changes in sea-surface hydrography during the last 85,000 yr. Warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high XRF intensities of Ti and Fe, and which suggest humid conditions in northeast Brazil. These tropical signals correlate with climatic oscillations recorded in Greenland ice cores (Dansgaard-Oeschger cycles) and in sediment cores from the North Atlantic (Heinrich events). Trade winds may have caused changes in the North Brazil Current that altered heat and salt flux into the North Atlantic, thus affecting the growth and decay of the large glacial ice sheets.

scholarly journals Synchronizing the Greenland ice core and radiocarbon timescales over the Holocene – Bayesian wiggle-matching of cosmogenic radionuclide records

2016 ◽  
Vol 12 (1) ◽  
pp. 15-30 ◽  
Author(s):  
F. Adolphi ◽  
R. Muscheler
Keyword(s):  
Statistical Approach ◽  
Ice Core ◽  
Ice Cores ◽  
The Holocene ◽  
Counting Error ◽  
Climate Reconstructions ◽  
Uncertainty Measurement ◽  
Uncertainty Estimates ◽  
Paleoclimate Records ◽  
Cosmogenic Radionuclide

Abstract. Investigations of past climate dynamics rely on accurate and precise chronologies of the employed climate reconstructions. The radiocarbon dating calibration curve (IntCal13) and the Greenland ice core chronology (GICC05) represent two of the most widely used chronological frameworks in paleoclimatology of the past  ∼  50 000 years. However, comparisons of climate records anchored on these chronologies are hampered by the precision and accuracy of both timescales. Here we use common variations in the production rates of 14C and 10Be recorded in tree-rings and ice cores, respectively, to assess the differences between both timescales during the Holocene. Compared to earlier work, we employ a novel statistical approach which leads to strongly reduced and yet, more robust, uncertainty estimates. Furthermore, we demonstrate that the inferred timescale differences are robust independent of (i) the applied ice core 10Be records, (ii) assumptions of the mode of 10Be deposition, as well as (iii) carbon cycle effects on 14C, and (iv) in agreement with independent estimates of the timescale differences. Our results imply that the GICC05 counting error is likely underestimated during the most recent 2000 years leading to a dating bias that propagates throughout large parts of the Holocene. Nevertheless, our analysis indicates that the GICC05 counting error is generally a robust uncertainty measurement but care has to be taken when treating it as a nearly Gaussian error distribution. The proposed IntCal13-GICC05 transfer function facilitates the comparison of ice core and radiocarbon dated paleoclimate records at high chronological precision.

scholarly journals Surface mass balance and water stable isotopes derived from firn cores on three ice rises, Fimbul Ice Shelf, Antarctica

2016 ◽  
Vol 10 (6) ◽  
pp. 2763-2777 ◽  
Author(s):  
Carmen P. Vega ◽  
Elisabeth Schlosser ◽  
Dmitry V. Divine ◽  
Jack Kohler ◽  
Tõnu Martma ◽  
...  
Keyword(s):  
High Resolution ◽  
Stable Isotope ◽  
Mass Balance ◽  
Temporal Variability ◽  
Ice Cores ◽  
Surface Mass Balance ◽  
Ice Shelf ◽  
Climate Signal ◽  
Surface Mass ◽  
Water Stable Isotope

Abstract. Three shallow firn cores were retrieved in the austral summers of 2011/12 and 2013/14 on the ice rises Kupol Ciolkovskogo (KC), Kupol Moskovskij (KM), and Blåskimen Island (BI), all part of Fimbul Ice Shelf (FIS) in western Dronning Maud Land (DML), Antarctica. The cores were dated back to 1958 (KC), 1995 (KM), and 1996 (BI) by annual layer counting using high-resolution oxygen isotope (δ18O) data, and by identifying volcanic horizons using non-sea-salt sulfate (nssSO42−) data. The water stable isotope records show that the atmospheric signature of the annual snow accumulation cycle is well preserved in the firn column, especially at KM and BI. We are able to determine the annual surface mass balance (SMB), as well as the mean SMB values between identified volcanic horizons. Average SMB at the KM and BI sites (0.68 and 0.70 mw. e. yr−1) was higher than at the KC site (0.24 mw. e. yr−1), and there was greater temporal variability as well. Trends in the SMB and δ18O records from the KC core over the period of 1958–2012 agree well with other previously investigated cores in the area, thus the KC site could be considered the most representative of the climate of the region. Cores from KM and BI appear to be more affected by local meteorological conditions and surface topography. Our results suggest that the ice rises are suitable sites for the retrieval of longer firn and ice cores, but that BI has the best preserved seasonal cycles of the three records and is thus the most optimal site for high-resolution studies of temporal variability of the climate signal. Deuterium excess data suggest a possible effect of seasonal moisture transport changes on the annual isotopic signal. In agreement with previous studies, large-scale atmospheric circulation patterns most likely provide the dominant influence on water stable isotope ratios preserved at the core sites.

scholarly journals Historical Forest Management Practices Influence Tree-Ring Based Climate Reconstructions

2021 ◽  
Vol 9 ◽  
Author(s):  
Georgios Skiadaresis ◽  
Bernhard Muigg ◽  
Willy Tegel
Keyword(s):  
Forest Management ◽  
Tree Ring ◽  
Management Practices ◽  
Growth Patterns ◽  
Climate Control ◽  
Climate Signal ◽  
Forest Management Practices ◽  
Management Interventions ◽  
Climate Reconstructions ◽  
Historical Forest

Tree-ring widths (TRW) of historical and archeological wood provide crucial proxies, frequently used for high-resolution multi-millennial paleoclimate reconstructions. Former growing conditions of the utilized trees, however, are largely unknown. Potential influences of historical forest management practices on climatic information, derived from TRW variability need to be considered but have not been assessed so far. Here, we examined the suitability of TRW series from traditionally managed oak forests (Quercus spp.) for climate reconstructions. We compared the climate signal in TRW chronologies of trees originating from high forests and coppice-with-standards (CWS) forests, a silvicultural management practice widely used in Europe for most of the common era. We expected a less distinct climate control in CWS due to management-induced growth patterns, yet an improved climate-growth relationship with TRW data from conventionally managed high forests. CWS tree rings showed considerably weaker correlations with hydroclimatic variables than non-CWS trees. The greatest potential for hydroclimate reconstructions was found for a large dataset containing both CWS and non-CWS trees, randomly collected from lumber yards, resembling the randomness in sources of historical material. Our results imply that growth patterns induced by management interventions can dampen climate signals in TRW chronologies. However, their impact can be minimized in well replicated, randomly sampled regional chronologies.

scholarly journals Glacial–interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ<sup>15</sup>N measurements

2013 ◽  
Vol 9 (3) ◽  
pp. 983-999 ◽  
Author(s):  
E. Capron ◽  
A. Landais ◽  
D. Buiron ◽  
A. Cauquoin ◽  
J. Chappellaz ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Detailed Comparison ◽  
Last Deglaciation ◽  
Depth Study ◽  
Dronning Maud Land ◽  
The Last Deglaciation ◽  
Correct Estimation ◽  
Lock In

Abstract. Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial–interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML – a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas–ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model–δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

Estimating the diffusion length in the deepest section of ice cores; A case study for MIS19 in Dome-C

2021 ◽  
Author(s):  
Thomas Laepple ◽  
Thomas Münch ◽  
Torben Kunz ◽  
Mathieu Casado ◽  
Maria Hoerhold
Keyword(s):  
Diffusion Length ◽  
Ice Core ◽  
Ice Cores ◽  
Climate Information ◽  
Climate Signal ◽  
A Value ◽  
Recovery Strategies ◽  
Length Estimate ◽  
And Diffusion

&lt;p&gt;To recover very old climate information from ice core records, one needs to interpret the deepest part of an ice core. As the oldest record, the Dome-C ice core can serve as an analogue for the Beyond EPICA Oldest Ice Core that is currently being drilled.&lt;br&gt;&lt;br&gt;Pol et al., EPSL 2010 analyzed high resolution water isotope data from the Dome-C ice core and found evidence for a limited preservation of climate variability in the deep section of the core due to mixing and diffusion. For instance, for Marine Isotope Stage 19, the study estimated a mixing/diffusion length between 40 and 60 cm, a value more than double than&amp;#160;what is&amp;#160;predicted by current firn and&amp;#160;ice diffusion&amp;#160;models. Knowing the diffusion length is important to interpret the isotope signal and is the basis to deconvolve climate records. As a result, it is key to bridge the gap in the estimation of the diffusion length between potentially biased statistical methods and firn and ice diffusion models.&lt;br&gt;We review this diffusion length estimate for MIS19, and also outline a new&amp;#160;general&amp;#160;method how to estimate the diffusion length in&amp;#160;highly thinned deep ice.&amp;#160; This approach presents&amp;#160;an important tool for better characterizing the preservation of the climate signal in old ice&amp;#160;and thus&amp;#160;for&amp;#160;designing optimal sampling and recovery strategies.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Global biosphere primary productivity over the last 800,000 years reconstructed from the triple-isotope composition of dioxygen trapped in polar ice cores

2021 ◽  
Author(s):  
Ji-Woong Yang ◽  
Amaëlle Landais ◽  
Margaux Brandon ◽  
Thomas Blunier ◽  
Frédéric Prié ◽  
...  
Keyword(s):  
Primary Productivity ◽  
Isotope Composition ◽  
Atmospheric Oxygen ◽  
Ice Cores ◽  
Oxygenic Photosynthesis ◽  
Time Interval ◽  
Polar Ice ◽  
Future Evolution ◽  
Glacial Stage ◽  
Glacial Periods

&lt;p&gt;The primary production, or oxygenic photosynthesis of the global biosphere, is one of the main source and sink of atmospheric oxygen (O&lt;sub&gt;2&lt;/sub&gt;) and carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;), respectively. There has been a growing number of evidence that global gross primary productivity (GPP) varies in response to climate change. It is therefore important to understand the climate- and/or environment controls of the global biosphere primary productivity for better predicting the future evolution of biosphere carbon uptake. The triple-isotope composition of O&lt;sub&gt;2&lt;/sub&gt; (&amp;#916;&lt;sup&gt;17&lt;/sup&gt;O of O&lt;sub&gt;2&lt;/sub&gt;) trapped in polar ice cores allows us to trace the past changes of global biosphere primary productivity as far back as 800,000 years before present (800 ka). Previously available &amp;#916;&lt;sup&gt;17&lt;/sup&gt;O of O&lt;sub&gt;2&lt;/sub&gt; records over the last ca. 450 ka show relatively low and high global biosphere productivity over the last five glacial and interglacial intervals respectively, with a unique pattern over Termination V (TV) - Marine Isotopic Stage (MIS) 11, as biosphere productivity at the end of TV is ~ 20 % higher than the four younger ones (Blunier et al., 2012; Brandon et al., 2020). However, questions remain on (1) whether the concomitant changes of global biosphere productivity and CO&lt;sub&gt;2&lt;/sub&gt; were the pervasive feature of glacial periods over the last 800 ka, and (2) whether the global biosphere productivity during the &amp;#8220;lukewarm&amp;#8221; interglacials before the Mid-Brunhes Event (MBE) were lower than those after the MBE.&lt;br&gt;Here, we present an extended composite record of &amp;#916;&lt;sup&gt;17&lt;/sup&gt;O of O&lt;sub&gt;2&lt;/sub&gt; covering the last 800 ka, based on new &amp;#916;&lt;sup&gt;17&lt;/sup&gt;O of O&lt;sub&gt;2&lt;/sub&gt; results from the EPICA Dome C and reconstruct the evolution of global biosphere productivity over that time interval using the independent box models of Landais et al. (2007) and Blunier et al. (2012). We find that the glacial productivity minima occurred nearly synchronously with the glacial CO&lt;sub&gt;2&lt;/sub&gt; minima at mid-glacial stage; interestingly millennia before the sea level reaches their minima. Following the mid-glacial minima, we also show slight productivity increases at the full-glacial stages, before deglacial productivity rises. Comparison of reconstructed interglacial productivity demonstrates a slightly higher productivity over the post-MBE (MISs 1, 5, 7, 9, and 11) than pre-MBE ones (MISs 13, 15, 17, and 19). However, the mean difference between post- and pre-MBE interglacials largely depends on the box model used for productivity reconstruction.&lt;/p&gt;

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