C. Atkins

Orbitally induced oscillations in the East Antarctic ice sheet at the Oligocene/Miocene boundary

Between 34 and 15 million years (Myr) ago, when planetary temperatures were 3–4 °C warmer than at present and atmospheric CO2 concentrations were twice as high as today, the Antarctic ice sheets may have been unstable. Oxygen isotope records from deep-sea sediment cores suggest that during this time fluctuations in global temperatures and high-latitude continental ice volumes were influenced by orbital cycles. But it has hitherto not been possible to calibrate the inferred changes in ice volume with direct evidence for oscillations of the Antarctic ice sheets. Here we present sediment data from shallow marine cores in the western Ross Sea that exhibit well dated cyclic variations, and which link the extent of the East Antarctic ice sheet directly to orbital cycles during the Oligocene/Miocene transition (24.1–23.7 Myr ago). Three rapidly deposited glacimarine sequences are constrained to a period of less than 450 kyr by our age model, suggesting that orbital influences at the frequencies of obliquity (40 kyr) and eccentricity (125 kyr) controlled the oscillations of the ice margin at that time. An erosional hiatus covering 250 kyr provides direct evidence for a major episode of global cooling and ice-sheet expansion about 23.7 Myr ago, which had previously been inferred from oxygen isotope data (Mi1 event).

Cold glaciers erode and deposit: Evidence from Allan Hills, Antarctica

Here we report previously undescribed features of erosion and deposition by a cold (polar) glacier. A recent study challenged the assumption that cold glaciers neither slide nor abrade their beds, but no geological evidence was offered. The features we describe include abrasion marks, subglacial deposits, glaciotectonically deformed substrate, isolated blocks, ice-cored debris mounds, and boulder trains, all products of a recent cold ice advance and retreat. Mapping these features elsewhere in Antarctica will document recent shifts in the East Antarctic Ice Sheet margin, providing new insight on regional mass-balance changes.

The contribution of aeolian sand and dust to iron fertilization of phytoplankton blooms in southwestern Ross Sea, Antarctica

Iron is a limiting micronutrient for primary production in the Ross Sea, Antarctica. Recent observations reveal low dissolved Fe (dFe) concentrations in the Ross Sea polynya following high initial rates of primary production in summer, after the dFe winter reserve has been consumed. Significant new sources of dFe are therefore required to further sustain phytoplankton blooms. Iron from aeolian sand and dust (ASD) released from melting sea ice is one potential source. To constrain aeolian Fe inputs, we determined ASD mass accumulation rates and the total and soluble Fe content of ASD on sea ice in McMurdo Sound, southwestern (SW) Ross Sea. The mean mass accumulation rate was ~1.5 g m−2 yr−1, total Fe content of this ASD was 4 ± 1 wt %, and the percentage of soluble Fe was 11 ± 1%. Our mean estimate of the bulk aeolian dFe flux of 122.1 µmol m−2 yr−1 for the McMurdo Sound region suggests that aeolian Fe can support between 9.0 × 109 and 4.1 × 1011 mol C yr−1 (0.1–4.9 Tg C yr−1) of new primary production. This equates to only ~15% of new primary production in the SW Ross Sea, suggesting that aeolian dFe is a minor component of seasonal Fe supply. The very high ASD accumulation on sea ice in McMurdo Sound compared to other regions of Antarctica suggests that our results represent the upper limit of dFe supply to the ocean from this source in the Ross Sea.

Geomorphological evidence of cold-based glacier activity in South Victoria Land, Antarctica

Abstract Cold-based glaciers have long been recognized as capable of covering and protecting landscapes. However, recent studies of modern cold-based glaciers in Antarctica show that, in some situations, erosion, deformation and deposition can occur. Recognizing the dual ability of cold-based glaciers to protect and preserve surfaces on the one hand and erode and modify on the other is important for correctly interpreting the often-subtle imprint of cold-based glaciers on landscapes. A range of geomorphological features related to cold-based glacier activity has now been documented along with an improved understanding of cold-based glacier structure, processes and interaction with various substrates. Collectively, this provides an enhanced ability to understand the impact of cold-based glaciers on landscapes and reappraise the geomorphological record. Such insight allows recognition of previously unknown glacial events and better interpretations of the landscape exposure record. This is particularly important at the margins of the Antarctic Ice Sheets, where past fluctuations in ice sheet volume and its contributions to post glacial sea-level rise are poorly constrained. This paper reviews the known geomorphological evidence associated with cold-based glaciers in the South Victoria Land region of the Transantarctic Mountains. It aims to provide progress towards a set of criteria for recognizing cold-based glacier activity in other regions and to highlight the implications of cold-based glacial activity for surface exposure studies and interpreting glacial history.

Paleocene–Eocene stratigraphy and paleoenvironment at Tora, Southeast Wairarapa, New Zealand

The Upper Cretaceous and Lower Paleogene sedimentary rocks at Tora, southeast Wairarapa, are considered to form a transitional sedimentary succession within the East Coast Basin, containing elements of both the siliciclastic succession to the north in the eastern North Island and the pelagic succession to the south in eastern Marlborough. However, the Tora succession is complicated by rapid lateral facies changes, numerous unconformities and unusual occurrences of coarse-grained facies in what is more typically a rather monotonous fine-grained passive-margin sequence. We interpret the uppermost Cretaceous and Paleocene units (Manurewa, Awhea, Mungaroa and Awheaiti formations) as components within a middle to lower bathyal, submarine channel and fan complex that unconformably overlies the Upper Cretaceous Rakauroa Member of the Whangai Formation. The two overlying Lower–Upper Eocene units (Pukemuri Siltstone, Wanstead Formation) both consist of a basal debris-flow deposit grading into middle bathyal mudstone, deposited during progressive marine transgression and deepening to lower bathyal–abyssal depths.

The origin of lithogenic sediment in the south-western Ross Sea and implications for iron fertilization

Abstract Summer iron (Fe) fertilization in the Ross Sea has previously been observed in association with diatom productivity, lithogenic particles and excess Fe in the water column. This productivity event occurred during an early breakout of sea ice via katabatic winds, suggesting that aeolian dust could be an important source of lithogenic Fe required for diatom growth in the Ross Sea. Here we investigate the provenance of size-selected dust deposited on sea ice in McMurdo Sound, south-western (SW) Ross Sea. The isotopic signature of McMurdo Sound dust (0.70533<87Sr/86Sr<0.70915 and -1.1<εNd(0)<3.45) confirms that dust is locally sourced from the McMurdo Sound debris bands and comprises a two-component mixture of McMurdo Volcanic Group and southern Victoria Land lithologies. In addition, the provenance of lithogenic sediment trapped in the water column was investigated, and the isotopic signature (εNd(0)=3.9, 87Sr/86Sr=0.70434) is differentiated from long-range transported dust originating from South America and Australia. Elevated lithogenic accumulation rates in deeper sediment traps in the Ross Sea suggest that sinking particles in the water column cannot simply result from dust input at the surface. This discrepancy can be best explained by significant upwelling and remobilization of lithogenic Fe from the sea floor.

New stratigraphic constraints on the late Miocene–early Pliocene tectonic development of the Aorangi Range, Wairarapa

ABSTRACT A revised stratigraphy is presented for the late Miocene–early Pliocene sedimentary rocks of the northern Aorangi Range, Wairarapa. Despite major differences in lithology, the Clay Creek Limestone and Bells Creek Mudstone are shown to be partially coeval, while the overlying Makara Greensand is shown to be a diachronous unit that ranges from late Miocene (Kapitean) to early Pliocene (Opoitian) age. This revised stratigraphy raises questions about the current classification of the Palliser and Onoke groups, and provides new insights into regional geological history. Previous seismic imaging studies have identified an episode of accelerated crustal shortening and deformation in the Wairarapa region near the Miocene–Pliocene boundary. The Clay Creek Limestone has proven to be a useful marker horizon for constraining the timing and style of this deformational episode, which is interpreted to have occurred prior to 7.2 Ma.

Protecting Antarctica’s geological heritage

Since the International Geophysical Year (1957/58), conservation of sites of biological and ecological significance has been an important objective for many nations active in the Antarctic. Although conservation, as such, was not considered in the original Antarctic Treaty provisions in 1961, it was soon introduced through the AgreedMeasures developed in 1964. The designation of particular areas, initially to protect scientific research and then to conserve key examples of Antarctic habitats, was a cause supported by the Scientific Committee on Antarctic Research (SCAR) and agreed by Treaty Parties in the form of Sites of Special Scientific Interest (SSSI) and then Specially Protected Areas (SPA). At that stage non-biological sites could not be designated as SPAs and it took until 1989 for the Parties to recognize this might be necessary for outstanding geological sites and establish Specially Reserved Areas (SRA) of which only one the Dufek Massif in the Pensacola Mountains was ever designated. The Protocol on Environmental Protection to the Antarctic Treaty agreed in 1991 attempted to rationalize the protected area system by merging all the SSSI, SPA and SRA sites into a single system called Antarctic Specially Protected Areas (ASPAs) and redefined its scope to allow outstanding geological and geomorphological areas to be considered. This opened the way for earth scientists to propose geological sites for protection, such as important fossil sites for example, but there was concern that this approach might attract attention to important sites and result in increased damage and souveniring from tourism. Even so, geological heritage (or ‘geo-heritage’) remained almost completely outside the formal protected area system. With both tourism and researcher numbers increasing it was noticed that Antarctic fossils were being offered for sale indicating that potentially priceless material might be being pilfered from important Antarctic sites. There was also an increasing threat to the continent’s geological values from human activities such as oversampling by scientists, damage by infrastructure construction and impact from foot or vehicular traffic as the number of scientific stations and tourism landing sites increased. The need for recognition, proactive protection and management of geo-heritage in the Antarctic was becoming increasingly obvious and pressing. Despite the opportunities presented by the Protocol little has been done in the past 25 years to protect geological sites in spite of the numerous excellent, and globally significant, examples worthy of recognition and protection. Of the 72 ASPAs currently agreed, only 7% were designated with geological features as the primary values for protection. With geo-conservation actively developing in many other parts of the world, the lack of initiative in the Antarctic might simply be due to a i) lack of widespread awareness of geological heritage values and issues, or ii) a reluctance amongst geoscientists to designate, promote and champion geologically significant places as ASPAs. To provide the up-to-date scientific input necessary to rectify this lack of progress, the Geological Heritage andGeo-conservationActionGroup has been established by SCAR. Tasked with developing a range of criteria for identifying and classifying geological, paleontological and geomorphological sites of significance within Antarctica, the group will also develop sustainable management strategies and a code of conduct for geological field activities, with a view to balancing scientific research needs with long term conservation of geo-heritage, providing advice directly to the Committee for Environmental Protection. This Action Group provides an opportunity for all geoscientists to promote Antarctic geological heritage values and ensure that these features are recognized, valued and respected by future generations of scientists and visitors. Broad participation from the Antarctic science community is needed now to make rapid and significant progress.

Looking Back to the Future

Antarctica has not always been a frozen continent covered in large ice sheets. It has experienced vastly different climates, ranging from tropical to polar, over hundreds of millions of years. As climate changed, so did the types of plants and animals, the amount of ice, the composition of the air and water, and the geological processes depositing sediments. Traces of these changes became preserved in layers of rock and ice that accumulated over time. Detailed studies of these layers allow scientists to produce a picture of, or to reconstruct, environments and climate conditions that existed in the past and piece together how and why they changed.