My research is best described as an interdisciplinary approach that links climate variability and climate impacts; I study mechanisms by which human societies interact with climate variability (and resultant environmental change) over the last 1000 years. The goal of my research is to combine paleoclimate findings with information gleaned from historical archives and archeological studies to understand how decadal climate variability and associated impacts affect human societies. Quantification of human-climate interaction is a step towards understanding how climate variability and change will affect future generations, and for us to be able to formulate policies that govern agricultural, maritime, health and international relations. As such, my research is extremely interdisciplinary in nature and is best discussed when divided under two hats, although the knowledge from each half informs the other half.
My current and future focus is on historical climatology that uses paleoclimate applications and studying historical archival material through a systems approach and statistical lens. In the past, completed work mostly are earth focussed. For ease, I have divided my research into two parts: Historical climatology (current and future work) and geological (past research)
Historical climate variability and impacts projects
[I] Current projects
(A) Developing corals as historical environmental archives. Hermatypic corals grow continuously for 50-500 years in tropical regions; with clear annual density banding structures, corals act as unique archives of information pertaining to variation in environmental, climatological and coastal conditions over the historical time period. My research focusses on characterizing materials that are trapped in coral cavities and studying trapped matter in relation to historical changes climate, environment, and human activity in surrounding regions. Most of the existing techniques focus on characterizing material that is substituted in coral skeletons. However, coral skeletons have cavities that trap material in proportion to the suspend load in the water column. Our team is currently developing non-destructive methods together with imaging studies to characterize type and quantity of detrital material trapped in coral cavities. Our area of focus is the Caribbean and soon to be expanded into the Indian ocean.
(B) Climate variability and climate impacts in Central India over the last 1000 years. Climate variability and impacts of climate in India is poorly documented. As such, there is a need to understand climate variability, especially on timescales of human interest (10-100 years), over the last 1000 years- a time period during which dramatic historical events have taken place: From the advent of the Mughal period to the current day scenario. Did climate variability play a role in these events and if so, how? What can knowledge about climate variability and climate impacts of historical time periods tell us about adaptive capacities, migration, and conflict in a climatologically and culturally diverse and divided country? How can we use this information to shape relations with the SE Asia region and the world? Understanding climate variability and how environments respond to variability is critical and missing in this knowledge. My team is using lake studies combined with climate information extracted from archaeological material and archival material to address these questions over the past 1000 years. There is evidence of dramatic climate variability that impacted several regions in the drought-prone central India that most certainly affected the following trend of historical events. My team is focussed on understanding the role of climate in these events.
(C) Decadal variability in East African monsoon and human impacts. We use a combination of paleoclimate data, instrumental data, and model output to understand the cause of the decline of the 'long rains' in the region. withWe primarily attempt to understand the role of Atlantic variability to decadal patterns in these two monsoonal systems. The work is a collaborative effort with North Carolina State University to marry high-resolution paleoclimatology and climate modeling. I welcome collaboration from scholars of history to help inform climate impacts in the region.
(D) Climate history and climate impacts using geochemistry of dust signatures in alpine lakes in western and the southwestern United States. The time period since the last deglaciation (~ 10,000 years) resulted in the development of indigenous culture in the American southwest. While paleoclimate studies have focussed on understanding rainfall variability and loess deposition, there has been a lack of systems approach to studying the climate-land-human feedback in the region. In the current project collaborative project, we are aiming to understand the linkages described above by revisited some studied sites in relation to new sites that are mainly high alpine lakes (the record the history of dust deposition and thereby land use changes), paleoclimate modeling and historical artifacts. Primarily, we are interested in seeing if tornado frequency altered in the region and how might that have impacted the development of indigenous culture in the region.
[II] Completed climatological studies (interpretation continues in relation to historical information)
(A) Dust emissions from the Sahel regions: A dust record from the Red Sea. Mineral dust in the atmosphere is a response to changes in soil conditions in the source region- which is related closely to rainfall variability and human activity such as agricultural decision, land productivity, and land use policies. As such mineral dust is a tool of understanding human decisions of using land in the context of environmental and climatological variability in arid regions. Using radiogenically derived 4He in corals- a proxy for detrital materials trapped in skeleton- I derived a 300-year-old continuous record of mineral dust record in the northern Red Sea. [This work was conducted during my Ph.D and in association with collaborators at Scripps Oceanography and MIT and is in revision]. Interpretation of this record continues in relation to the history of the Sahel region of North Africa.
(B) A 1000 year record of African dust transport to the Carribean: African dust is transported across the Atlantic Ocean in 7-10 days by trade winds. Transport of mineral dust over long distances, however, is not only related to how much dust gets lofted into the atmosphere from relevant dust hot spots but also to atmospheric circulation patterns that in turn are modified heavily by sea surface temperatures. Mineral dust export or transport thus provides key information about shipping routes and changes of shipping routes in association to changes in circulation patterns. In a follow-up work to the Red Sea, that explored dust emissions from regions surrounding the Red Sea over the last 300 years, I explored dust export from north Africa to the Caribbean in relation to climate variability and human activity in the Atlantic region. There is scope to interpret this work in relation to climate impacts on both sides of the Atlantic ocean and maritime activities in the Atlantic. (This work is in revision)
Students, scholars, and collaborators interested in the above questions, please write to me!
The final assembly- accretion of the Indian cratonic block with the Gondwanaland. This is the only geologically focused work that I am pursuing with my undergraduate students, my father (a geologist) and planetary scientists at UCLA to understand processes and timescales over which the final accretion of the Gondwanaland- the accretion of Indian cratonic block ith the larger Gondwanaland- took place. I am studying tectonic processes and changes in environment the postdates the tectonic event by employing elemental geochemistry, precision dating techniques, and field methods. Our paper was recently accepted in LITHOS and we are presenting an abstract at AGU (2016)
(A) Reconstructing high-resolution history of carbonate deposition in the Pacific and Atlantic oceans across the mass extinction boundary of K-Pg using extraterrestrial dust as a constant flux proxy. In this work, I mainly explored timescales of recovery of marine ecosystems (carbonate deposition is sensitive to changes in marine chemistry that in turn is dependent on supply from the continents and modifications by marine ecosystems) in the wake of a major environmental stressor (meteorite impact) that resulted in the last mass extinction on Earth.
(B) A 6 million year record of sediment delivery to the Gadar Drift in the North Atlantic. Here, we generated a record of changes in the chemistry and amount of sediment delivery to the Gadar Drift- a key location that has shown to be sensitive to variations in ocean circulations patterns especially in relation to the growth of ice sheets in the Arctic. The work is currently in prep
(C) Reconstructing seawater chemistry over 500 Million years. In this work, conducted as a part of my postdoctoral work at UCLA, I reconstructed changes in seawater chemistry over the past 500 million years using carbonate veins embedded in mid-oceanic ridge basalts. I used clumped isotope thermometric techniques to deduce temperatures at which the carbonate veins formed and then used the seawater-like veins (those that formed at low temperatures) to reflect upon the Mg/Ca and Sr/Ca evolution of the seawater. In addition, I have also used in-situ beam techniques such as the ion probe, laser ablation, and the electron probe to measure Mg/Ca and Sr/Ca in well-preserved fossils. The precision of the beams helped map the variation of these ratios in the fossils and therefore constrain temperature by eliminating locations within the fossils that show effects of diagenesis.
SELECTED INVITED PRESENTATIONS
- ICE Talk at University of Colorado Boulder (November 2016)
- “Saharan dust preserving the drought history of the Sahel? Exploring the coupling between drought and dust in semi-arid regions. Washington and Lee University, Lexington, VA (February 2016)
- “A proposal to understand decadal and multi-decadal variability in drought and environmental changes in central India- an exercise in proxy data and observation calibration” Indian Institute of Human Settlements, Bangalore, India (October 2015)
- Exploring the coupling between mineral dust and drought on decadal timescales and longer: insights from proxy records and the late 20th century Sahel drought”. Environmental Studies Program, University of Colorado, Boulder (October 2015)
- “Drought in the Sahel: Insights from two new mineral dust records”. Department of Earth and Atmospheric Sciences, University of Houston (July 2015)
- “Drought in the Sahel: Insights from two new mineral dust records”. Department of Earth Sciences, University of Southern California (June 2015)
- “Drought in the Sahel: New Insights from Helium-4 based dust records”, Marine Earth and Atmospheric Sciences Department, North Carolina State University Colloquium (January 2015)
- "Can we improve the relationship between regional climate models and high-resolution historical climate data?" The University of Minnesota, Expeditions in computing climate change colloquium (July 2014)
- “High-resolution record of dust, droughts and climate – a paleoclimate perspective”, Pacific Northwest National Laboratory Seminar series (July 2013)
- Bhattacharya and L. Roeder. “Role of institutions in improving climate communication”. AGU Chapman conference on “Communicating climate science, a historic look into the future” (June 2013)
- K.Thomas, S. Datta and A. Bhattacharya. “Climate Change: What we know and where we go from here”. Invited talk at SITN Seminar, Harvard Medical School (May 2012)