Tripati Aradhna K.

No Thumbnail Available
Last Name
Tripati
First Name
Aradhna K.
ORCID

Filters

2013 - 2014 2
2
2
Reset filters

Settings

Search Results

Now showing 1 - 2 of 2
  • Article
    The influence of temperature and seawater carbonate saturation state on 13C–18O bond ordering in bivalve mollusks
    (Copernicus Publications on behalf of the European Geosciences Union, 2013-07-10) Eagle, Robert A. ; Eiler, John M. ; Tripati, Aradhna K. ; Ries, J. B. ; Freitas, P. S. ; Hiebenthal, C. ; Wanamaker, Alan D. ; Taviani, Marco ; Elliot, Mary ; Marenssi, S. ; Nakamura, K. ; Ramirez, P. ; Roy, K.
    The shells of marine mollusks are widely used archives of past climate and ocean chemistry. Whilst the measurement of mollusk δ18O to develop records of past climate change is a commonly used approach, it has proven challenging to develop reliable independent paleothermometers that can be used to deconvolve the contributions of temperature and fluid composition on molluscan oxygen isotope compositions. Here we investigate the temperature dependence of 13C–18O bond abundance, denoted by the measured parameter Δ47, in shell carbonates of bivalve mollusks and assess its potential to be a useful paleothermometer. We report measurements on cultured specimens spanning a range in water temperatures of 5 to 25 °C, and field collected specimens spanning a range of −1 to 29 °C. In addition we investigate the potential influence of carbonate saturation state on bivalve stable isotope compositions by making measurements on both calcitic and aragonitic specimens that have been cultured in seawater that is either supersaturated or undersaturated with respect to aragonite. We find a robust relationship between Δ47 and growth temperature. We also find that the slope of a linear regression through all the Δ47 data for bivalves plotted against seawater temperature is significantly shallower than previously published inorganic and biogenic carbonate calibration studies produced in our laboratory and go on to discuss the possible sources of this difference. We find that changing seawater saturation state does not have significant effect on the Δ47 of bivalve shell carbonate in two taxa that we examined, and we do not observe significant differences between Δ47-temperature relationships between calcitic and aragonitic taxa.
  • Article
    Alteration of volcaniclastic deposits at Minna Bluff : geochemical insights on mineralizing environment and climate during the Late Miocene in Antarctica
    (John Wiley & Sons, 2014-08-19) Antibus, Joanne V. ; Panter, Kurt S. ; Wilch, Thomas I. ; Dunbar, Nelia W. ; McIntosh, William C. ; Tripati, Aradhna K. ; Bindeman, Ilya N. ; Blusztajn, Jerzy S.
    Secondary minerals in volcaniclastic deposits at Minna Bluff, a 45 km long peninsula in the Ross Sea, are used to infer processes of alteration and environmental conditions in the Late Miocene. Glassy volcaniclastic deposits are altered and contain phillipsite and chabazite, low to high-Mg carbonates, chalcedony, and clay. The δ18O of carbonates and chalcedony is variable, ranging from −0.50 to 21.53‰ and 0.68 to 10.37‰, respectively, and δD for chalcedony is light (−187.8 to −220.6‰), corresponding to Antarctic meteoric water. A mean carbonate 87Sr/86Sr ratio of 0.70327 ± 0.0009 (1σ, n = 12) is comparable to lava and suggests freshwater, as opposed to seawater, caused the alteration. Minerals were precipitated at elevated temperatures (91 and 104°C) based on quartz-calcite equilibrium, carbonate 13C-18C thermometry (Δ47 derived temperature = 5° to 43°C) and stability of zeolites in geothermal systems (>10 to ∼100°C). The alteration was a result of isolated, ephemeral events involving the exchange between heated meteoric water and glass during or soon after the formation of each deposit. Near-surface evaporative distillation can explain 18O-enriched compositions for some Mg-rich carbonates and chalcedony. The δ18Owater calculated for carbonates (−15.8 to −22.9‰) reveals a broad change, becoming heavier between ∼12 and ∼7 Ma, consistent with a warming climate. These findings are independently corroborated by the interpretation of Late Miocene sedimentary sequences recovered from nearby sediment cores. However, in contrast to a cold-based thermal regime proposed for ice flow at core sites, wet-based conditions prevailed at Minna Bluff; a likely consequence of high heat flow associated with an active magma system.