Bengaluru: The Indian Scientific Expedition to the Southern Ocean (ISESO) 2020, which aims to improving predictions of future climate changes, collected this week the largest-ever ocean sediment core from the Southern Ocean — by an Indian mission.
Sediment cores are tubes of material from the Earth’s crust drilled up from the sea floor.
As changes occur in the climate and the ocean, it is reflected in sediments that settle on the surface over hundreds of thousands of years. A sediment core consists of layers of sediments that can be studied for their climate variability and properties.
The ISESO mission set sail in January on the research vessel S.A. Agulhas. The Agulhas entered the Antarctic circle on 8 February.
An 18-institution team led by Anoop Mahajan of the Indian Institute of Tropical Meteorology (IITM), Pune, is part of the expedition. The Southern Ocean Research Program is headed by Anil Kumar, group director of Ocean Sciences at National Centre for Polar and Ocean Research (NCPOR), Goa.
Scientists working on the sediment core project will analyse the core to understand how much the waters of the northern hemisphere interact with the southern, and if the sea surface temperature variation in the southern ocean affects the Indian Ocean.
Scientists onboard this mission aim to understand how the Southern Ocean is responding to the rapidly heating climate and what we can glean about the future from it.
The Southern Ocean core samples will be brought back to the labs at the NCPOR. Paleoceanographer Manish Tiwari is heading the project.
“Once a sediment core is extracted, we can study it to unravel various mechanisms causing climatic variability in that region during that particular time period,” Tiwari told ThePrint.
“It would help to understand the role these regions, such as the Southern Ocean, play in the global climate dynamics.”
To extract these core samples, specially designed ‘corers’ are drilled and inserted into the ocean floor. These ‘corers’ have weights on top to facilitate faster penetration through soft sediments of the ocean.
The core sizes are measured in length, indicating how far the floor was dug. The current core’s size was 3.5 metres, which is the largest Southern Ocean core India will possess.
This size is important because “as we go down in a sediment core, we go further and further back in time,” said Tiwari.
This core sample can enable us to study climate processes up until a 1,00,000 years ago to maybe even a million years ago, once dating has been done.
Once the core is on the ship and stored securely, its processing will first begin by slicing the core from the top into thin discs that are as small as mere millimetres in thickness. This core sample will be cut into a resolution of 1 centimetre. This extraction is done by specialised equipment to facilitate precise measurements.
The collected soft mud will then be transferred into sample bags, which will be sealed on the ship and reopened in Goa.
Tiwari explained: “The composition of the sediment decide how it looks.”
“If it is rich in carbonate, then it will appear whitish and if it is rich in organic matter or clay, it would appear dark.”
The very first bit of analysis that will be done is radiocarbon dating to determine how far into the past we can see from the samples and how many years each sample covers.
Then stable isotopes of carbon and oxygen are studied for each sample. These help to determine the temperature and salinity of samples at the time they were being deposited on the ocean floor. This can then be used to calculate how much ice melted (i.e., how much freshwater entered the salty ocean), how the rainfall was, etc. Thus, these are called climatic proxies.
Carbon and oxygen content is studied in both carbonate and sea water samples. Carbonate shells made up of calcium carbonate are produced by many species of microfossils (foraminifera).
“These shells are made up of calcium carbonate so they store in themselves the signature of carbon & oxygen isotopes of the seawater in which they precipitate their shells,” explained Tiwari.
“Thus they act as powerful proxies, which help in reconstructing past seawater characteristics that is directly linked to Earth’s climatic history. The variability in these isotopes is relatable to salinity, productivity etc. that can indicate about precipitation, wind strength etc.”
“Proxies are parameters that record the signature of climate of that time,” he added.
Using the data obtained from this core and from existing research, the scientists can deduce not only how the Southern Ocean has adapted to changes in the climate in the past, but also how Indian monsoon patterns correlate with the said changes.
The latest core was collected from a location on the Ocean at 65 degree S, 74 degree E, just around 500 km northwest of Davis Station on Antarctica.
The mission will in total collect three sediment cores, spread hundreds of kilometres apart before the Agulhas returns to India.