Dronning Maud Land Ice Core Research Articles

Identifying the provenance and quantifying the contribution of dust sources in EPICA Dronning Maud Land ice core (Antarctica) over the last deglaciation (7–27 kyr BP): A high-resolution, quantitative record from a new Rare Earth Element mixing model

Antarctic ice cores have revealed the interplay between dust and climate in the Southern Hemisphere. Yet, so far, no continuous record of dust provenance has been established through the last deglaciation. Here, using a new database of 207 Rare Earth Element (REE) patterns measured in dust and sediments/soils from well-known potential source areas (PSA) of the Southern Hemisphere, we developed a statistical model combining those inputs to provide the best fit to the REE patterns measured in EPICA Dronning Maud Land (EDML) ice core (E. Antarctica). Out of 398 samples measured in the EDML core, 386 samples have been un-mixed with statistical significance. Combined with the total atmospheric deposition, we quantified the dust flux from each PSA to EDML between 7 and 27 kyr BP. Our results reveal that the dust composition was relatively uniform up until 14.5 kyr BP despite a large drop in atmospheric deposition at ∼18 kyr with a large contribution from Patagonia yielding ∼68 % of total dust deposition. The remaining dust was supplied from Australia (14–15 %), Southern Africa (∼9 %), New Zealand (∼3–4 %) and Puna-Altiplano (∼2–3 %). The most striking change occurred ∼14.5 kyr BP when Patagonia dropped below 50 % on average while low-latitude PSA increased their contributions to 21–23 % for Southern Africa, 13–21 % for Australia and ∼ 4–10 % for Puna-Altiplano. We argue that this shift is linked to long-lasting changes in the hydrology of Patagonian rivers and to sudden acceleration of the submersion of Patagonian shelf at 14.5 kyr BP, highlighting a relationship between dust composition and eustatic sea level. Early Holocene dust composition is highly variable, with Patagonian contribution being still prevalent, at ∼50 % on average. Provided a good coverage of local and distal PSA, our statistical model based on REE pattern offers a straightforward and cost-effective method to trace dust source in ice cores.

Can Ammonium Records in Antarctic Ice Cores be a Proxy for Sea Ice Fluctuations?

Abstract Ammonium (NH4+) accumulation and variability in Antarctic ice cores possess signals of various biological, anthropogenic, and atmospheric processes. However, the use of NH4+ variability in Antarctic ice cores for paleoclimate reconstructions is not well established. Addressing this, we have utilized, published NH4+ ice core records from the Dronning Maud Land (DML), Antarctica to assess the sources of NH4+, its transport, major forcing factors, and their mechanism in controlling the variability of ammonium signals in coastal ice cores. The first principle component (PC1) derived from PC analysis of NH4+ data comprises ~43% of total variability and also depicts a significant spatial correlation with the NSIDC Sea ice concentration (SIC) variability in the Weddell Sea region of the Southern Ocean. In addition, the PC1 shows strong 2-9 year periodicities related to El Niño Southern Oscillation along with two major decadal to centennial periodicities of ~40 and 100 years. The control of sea ice fluctuations and related oceanic processes (ENSO) provide evidence of the marine sources and influence of ocean-related processes as a major controlling factor for the NH4+ variability in DML ice cores. The cumulative accumulation of the NH4+ produced from enhanced biological decomposition, and unutilized ammonium during nitrification under high SIC conditions are possible mechanisms for the increased supply. The correlation of ERA5 surface air temperatures with Nino3.4 suggests that during El Niño conditions, the air temperatures significantly dropped in the Weddell Sea sector, fostering the high SIC conditions. The findings of this study regarding the role of the SIC in the ammonium variability in Antarctic ice cores would help us better interpret the paleo NH4+ records and their applications to deduce the paleoclimate conditions in coastal Antarctic regions.

The role of seasonality of mineral dust concentration and size on glacial/interglacial dust changes in the EPICA Dronning Maud Land ice core

AbstractWe present a record of particulate dust concentration and size distribution in subannual resolution measured on the European Project for Ice Coring in Antarctica (EPICA) Dronning Maud Land (EDML) ice core drilled in the Atlantic sector of the East Antarctic plateau. The record reaches from present day back to the penultimate glacial until 145,000 years B.P. with subannual resolution from 60,000 years B.P. to the present. Mean dust concentrations are a factor of 46 higher during the glacial (~850–4600 ng/mL) compared to the Holocene (~16–112 ng/mL) with slightly smaller dust particles during the glacial compared to the Holocene and with an absolute minimum in the dust size at 16,000 years B.P. The changes in dust concentration are mainly attributed to changes in source conditions in southern South America. An increase in the modal value of the dust size suggests that at 16,000 years B.P. a major change in atmospheric circulation apparently allowed more direct transport of dust particles to the EDML drill site. We find a clear in‐phase relation of the seasonal variation in dust mass concentration and dust size during the glacial (r(conc,size) = 0.8) but no clear phase relationship during the Holocene (0 < r(conc,size) < 0.4). With a simple conceptual 1‐D model describing the transport of the dust to the ice sheet using the size as an indicator for transport intensity, we find that the effect of the changes in the seasonality of the source emission strength and the transport intensity on the dust decrease over Transition 1 can significantly contribute to the large decrease of dust concentration from the glacial to the Holocene.

Potential influence of temperature changes in the Southern Hemisphere on the evolution of the Asian summer monsoon during the last glacial period

A precisely 230Th-dated δ18O record of a stalagmite from Yangkou Cave, Chongqing, southwest China, is proposed to reconstruct the evolution of the East Asian summer monsoon (EASM) during the last glacial period (LGP) from 37.8 to 48.7 ka BP. The δ18O record reveals Dansgaard/Oeschger (D/O) 8–12 and Heinrich (H4, H5) climatic events. The inferred D/O events at EASM territory do not exhibit the asymmetrical feature of “rapid warming, slow cooling” recorded in Greenland ice cores. The Yangkou record is consistent with other records of Hulu and Xiaobailong Caves in the Chinese monsoon realm. Changes in the period from D/O 12 to D/O 9 and H4 events in the stalagmites is similar to the temperature changes recorded in the European Project for Ice Coring in Antarctica (EPICA) Dronning Maud Land Ice core (EDML). This similarity implies that Southern Hemisphere thermal condition could affect the EASM, the location of the Intertropical Convergence Zone (ITCZ), and also the Hadley circulation. Changes in D/O 12 and the end of the H5 in Chinese records are different from those in Socotra Island, located in the Indian summer monsoon (ISM) region, which are concurrent with NGRIP records. During the H5 period, in the Southern Hemisphere, temperature increased gradually to a maximum and the Hadley circulation intensity in the Southern Hemisphere decreased. Simultaneously, the southeast trade winds in the Southern Hemisphere gradually weakened, resulting in the weakening of the ISM and eventually the weakest ISM at ∼47.2 ka BP. Our records support that the evolution of the summer monsoon in the low-latitude Asian zones was not only affected by summer insolation and climatic changes in the high latitudes of the Northern Hemisphere but also by temperature changes in the Southern Hemisphere.

Duration of Greenland Stadial 22 and ice-gas Δage from counting of annual layers in Greenland NGRIP ice core

Abstract. High-resolution measurements of chemical impurities and methane concentrations in Greenland ice core samples from the early glacial period allow the extension of annual-layer counted chronologies and the improvement of gas age-ice age difference (Δage) essential to the synchronization of ice core records. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses in order to constrain the duration of the Greenland Stadial 22 (GS-22) between Greenland Interstadials (GIs) 21 and 22, for which inconsistent durations and ages have been reported from Greenland and Antarctic ice core records as well as European speleothems. Depending on the chronology used, GS-22 occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21). From annual layer counting, we find that GS-22 lasted between 2696 and 3092 years and was followed by a GI-21 pre-cursor event lasting between 331 and 369 yr. Our layer-based counting agrees with the duration of stadial 22 as determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr) or an alternative chronology based on gas-marker synchronization to EPICA Dronning Maud Land ice core. These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the possible ranges of NorthGRIP Δdepth (5.49 to 5.85 m) and Δage (498 to 601 yr) at the warming onset of GI-21 as well as the Δage range at the onset of the GI-21 precursor warming (523 to 654 yr), observing that temperature (represented by the δ15N proxy) increases before CH4 concentration by no more than a few decades.

Centennial-scale climate variability in the Timor Sea during Marine Isotope Stage 3

We present a high-resolution (∼ 60–110 yr) multi-proxy record spanning Marine Isotope Stage 3 from IMAGES Core MD01-2378 (13°04.95′ S and 121°47.27′ E, 1783 m water depth), located in the Timor Sea, off NW Australia. Today, this area is influenced by the Intertropical Convergence Zone, which drives monsoonal winds during austral summer and by the main outflow of the Indonesian Throughflow, which represents a key component of the global thermohaline circulation system. Thus, this core is ideally situated to monitor the linkages between tropical and high latitude climate variability. Benthic δ 18O data ( Planulina wuellerstorfi) clearly reflect Antarctic warm events (A1–A4) as recorded by the EPICA Byrd and Dronning Maud Land ice cores. This southern high latitude signal is transferred by deep and intermediate water masses flowing northward from the Southern Ocean into the Indian Ocean. Planktonic δ 18O shows closer affinity to northern high latitudes planktonic and ice core records, although only the longer-lasting Dansgaard–Oeschger warm events, 8, 12, 14, and 16–17 are clearly expressed in our record. This northern high latitude signal in the surface water is probably transmitted through atmospheric teleconnections and coupling of the Asian–Australian monsoon systems. Benthic foraminiferal census counts suggest a coupling of Antarctic cooling with carbon flux patterns in the Timor Sea. We relate increasing abundances of carbon-flux sensitive species at 38–45 ka to the northeastward migration of the West Australian Current frontal area. This water mass reorganization is also supported by concurrent decreases in Mg/Ca and planktonic δ 18O values ( Globigerinoides ruber white).

One-to-one coupling of glacial climate variability in Greenland and Antarctica

Precise knowledge of the phase relationship between climate changes in the two hemispheres is a key for understanding the Earth's climate dynamics. For the last glacial period, ice core studies have revealed strong coupling of the largest millennial-scale warm events in Antarctica with the longest Dansgaard-Oeschger events in Greenland through the Atlantic meridional overturning circulation. It has been unclear, however, whether the shorter Dansgaard-Oeschger events have counterparts in the shorter and less prominent Antarctic temperature variations, and whether these events are linked by the same mechanism. Here we present a glacial climate record derived from an ice core from Dronning Maud Land, Antarctica, which represents South Atlantic climate at a resolution comparable with the Greenland ice core records. After methane synchronization with an ice core from North Greenland, the oxygen isotope record from the Dronning Maud Land ice core shows a one-to-one coupling between all Antarctic warm events and Greenland Dansgaard-Oeschger events by the bipolar seesaw6. The amplitude of the Antarctic warm events is found to be linearly dependent on the duration of the concurrent stadial in the North, suggesting that they all result from a similar reduction in the meridional overturning circulation.

Supporting evidence from the EPICA Dronning Maud Land ice core for atmospheric CO2 changes during the past millennium

The most direct method of investigating past variations of the atmospheric CO2 concentration before 1958, when continuous direct atmospheric CO2 measurements started, is the analysis of air extracted from suitable ice cores. Here we present a new detailed CO2 record from the Dronning Maud Land (DML) ice core, drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA) and some new measurements on a previously drilled ice core from the South Pole. The DML CO2 record shows an increase from about 278 to 282 parts per million by volume (ppmv) between ad 1000 and ad 1200 and a fairly continuous decrease to a mean value of about 277 ppmv around ad 1700. While the new South Pole measurements agree well with DML at the minimum at ad 1700 they are on average about 2 ppmv lower during the period ad 1000–1500. Published measurements from the coastal high-accumulation site Law Dome are considered as very reliable because of the reproducibility of the measurements, high temporal resolution and an accurate time scale. Other Antarctic ice cores could not, or only partly, reproduce the pre-industrial measurements from Law Dome. A comparison of the trends of DML and Law Dome shows a general agreement. However we should be able to rule out co-variations caused by the same artefact. Two possible effects are discussed, first production of CO2 by chemical reactions and second diffusion of dissolved air through the ice matrix into the bubbles. While the first effect cannot be totally excluded, comparison of the Law Dome and DML record shows that dissolved air diffusing to bubbles cannot be responsible for the pre-industrial variation. Therefore, the new record is not a proof of the Law Dome results but the first very strong support from an ice core of the Antarctic plateau.

Supporting evidence from the EPICA Dronning Maud Land ice core for atmospheric CO2 changes during the past millennium

The most direct method of investigating past variations of the atmospheric CO2 concentration before 1958, when continuous direct atmospheric CO2 measurements started, is the analysis of air extracted from suitable ice cores. Here we present a new detailed CO2record from the Dronning Maud Land (DML) ice core, drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA) and some new measurements on a previously drilled ice core from the South Pole. The DML CO2 record shows an increase from about 278 to 282 parts per million by volume (ppmv) between ad 1000 and ad 1200 and a fairly continuous decrease to a mean value of about 277 ppmv around ad 1700. While the new South Pole measurements agree well with DML at the minimum at ad 1700 they are on average about 2 ppmv lower during the period ad 1000–1500. Published measurements from the coastal high-accumulation site Law Dome are considered as very reliable because of the reproducibility of the measurements, high temporal resolution and an accurate time scale. Other Antarctic ice cores could not, or only partly, reproduce the pre-industrial measurements from Law Dome. A comparison of the trends of DML and Law Dome shows a general agreement. However we should be able to rule out co-variations caused by the same artefact. Two possible effects are discussed, first production of CO2 by chemical reactions and second diffusion of dissolved air through the ice matrix into the bubbles. While the first effect cannot be totally excluded, comparison of the Law Dome and DML record shows that dissolved air diffusing to bubbles cannot be responsible for the pre-industrial variation. Therefore, the new record is not a proof of the Law Dome results but the first very strong support from an ice core of the Antarctic plateau.