Meloth Thamban and Rasik Ravindra

Scrutiny of instrumental data from Antarctic reveals that the Continent has undergone significant changes in the recent decades, with an increase in atmospheric temperature in most parts. The largest annual warming trends are found in the West Antarctic and Antarctic Peninsula in particular. In contrast, the East Antarctic has experienced little warming. However, recent studies reveal that the warming had affected many sites in the coastal East Antarctic. Importantly, the complexity of Antarctic climate is still poorly understood because of the limited periods of observational data.

Annual scientific research expeditions to the Antarctic by the National Centre for Antarctic and Ocean Research (NCAOR), Goa, utilises its singular environment as a great natural laboratory for scientific investigations that assists the understanding of global environment change. India established its first station in Antarctic at Dakshin Gangotri in 1983, followed by the second permanent station at Maitri in 1989. A third station Bharati is being established at the Larsemann Hills area of East Antarctic.
The present study investigates the fluctuating Antarctic climate system on sub-annual to centennial time scales, with a complex interplay of the ice sheet, ocean, sea ice, and atmosphere. Scrutiny of instrumental data from Antarctic based on the few available records reveal that Antarctic had undergone significant changes in recent decades, with an increase in atmospheric temperature in most parts of the Antarctic continent. The largest annual warming trends are found on the western and northern parts of the Antarctic Peninsula. Contrastingly, interior parts of East Antarctic seems to have experienced little warming or even slight cooling at certain locations. However, the spatial and temporal complexity of Antarctic climate is still poorly understood because of the limited and short periods of observational data.
Analyses of ice core proxy records provide one of the most accurate methods to reconstruct the Antarctic climate change beyond the instrumental limits. Ice core records from polar regions offer continuous and highly resolved proxy records on major atmospheric parameters like temperature, composition and trace gases. Among the various proxy variables used, the stable isotope ratios of oxygen (d18O) and hydrogen (dD) offer the most critical information on the past changes in temperature. Additionally, glaciochemical parameters like ionic and trace metal composition of the ice cores are extensively used for reconstructing past changes in atmospheric circulation, global volcanism, dust input, sea ice extent/concentration, oceanic productivity, as well as environmental pollution.

ANTARCITC IS WARMING
Considering the importance of chronicling Antarctic environmental change in the context of global warming, Indian researchers have made systematic efforts to retrieve and study ice core records from the coastal regions of East Antarctic. Further to understand the coastal Antarctic variability during the past few centuries with annual to sub-annual resolution, several ice cores have been collected from the coastal sites of East Antarctic. Among these, two ice cores from the central Dronning Maud Land region (IND-22/B4 and IND-25/B5, Fig 2) with reliable chronological constraints were studied extensively for various proxy parameters. While the IND-25/B5 provided high-resolution records of the past 100 years (1905-2005), the IND-22/B4 core represented the past ~470 years (1530-2002) of climate change in coastal East Antarctic. The considerable variation in d18O records on an interannual to decadal scale seems to be associated with changes in low and mid latitude climatic modes. The IND-25/B5 d18O record revealed a significant relation to the Southern Annular Mode (SAM) and the El Niño Southern Oscillation (ENSO). Conversely, on a decadal scale, the influence of ENSO diminishes and a significant relationship between d18O and SAM is established. Application of the d18O-temperature relationship in the region to the IND-25/B5 ice core record revealed an average air temperature of -25.5°C during 1905-2005 AD. Compared to this, extended d18O records of IND-22/B4 revealed an average temperature of -19.3°C during 1530-2002.
The reconstructed temperature record of IND-25/B5 exhibited an average warming of 1°C for the entire century (1905-2005) with a warming trend of 0.1°C/10 years. The records also revealed a greatly enhanced warming of ~3°C during 1930-2005 (~0.4°C/10 years). The temperature record of IND-22/B4 exhibited relatively more negative d18O values during periods of reduced solar activity like the Dalton and Maunder Minima, suggesting significant influence of solar activity on Antarctic climate. The estimated warming trend for this site was ~0.6°C per century, with relatively increased warming during the recent decades.
The reconstructed temperature records of ice cores as well as the available observational data thus suggest that the coastal regions of Dronning Maud Land in East Antarctic are experiencing significant warming in the recent decades. The findings have considerable implications for the coastal Antarctic ice sheet stability and possible sea level changes. On a broader perspective, effects of such enhanced warming could affect the fragile Antarctic ecosystem. Any loss of sea ice due to warming could adversely affect the coastal Antarctic food chain system since any decrease in sea ice algae would affect the krill population, which in turn would affect the Adélie Penguin population.
Our studies while confirming the instrumental record of recent warming at the Novo Antarctic station data, contradict the observed slight cooling at the South Pole Amundsen-Scott Station. Considering such large spatial and temporal heterogeneity in the environmental conditions, the current estimation of temperature trends across the East Antarctic based on extrapolations using few station records needs to be vigorously tested. It is suggested that spatially distributed ice core derived temperature profiles could provide valuable data in filling the large gaps as well as extending the climatic records in Antarctic.

The author are Scientist E and Director, respectively at the National Centre for Antarctic and Ocean Research, Goa. meloth@ncaor.org