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Papers by Cassandre Stirpe

Water Air and Soil Pollution, Sep 1, 2017

Salt applied to roads for de-icing can persist for decades in watersheds, and understanding rates... more Salt applied to roads for de-icing can persist for decades in watersheds, and understanding rates of salt accumulation and export is important for anticipating the magnitude and duration of its environmental impacts. Salt removal is affected by storm frequency and intensity, both of which are projected to change as a result of anthropogenic climate change. To examine the potential outcomes of changing storm regimes on rates of salt export from watersheds, we studied chloride concentrations in baseflow and surface runoff in 5 years of streamflow data (taken at 20-min intervals) in a headwater tributary of the Hudson River. Baseflow, with chloride concentrations of 200–230 mg/L year-round, dominated streamflow, except during and after large storms, and accounted for about 90% of chloride export from the watershed. Extreme precipitation events (e.g., tropical storms) increased salt export mainly by increasing baseflow discharge, which remained elevated long after storms ended. While intense events accomplished more salt export per storm, they did not produce disproportionately higher export per volume of precipitation, compared to smaller rain events. Chloride export in a wet year was almost twice that in a dry year, despite less than a doubling of rainfall. Under future climate conditions, if winter precipitation shifts toward a higher proportion of rainfall, or summers experience a greater frequency of tropical storms, then long-term residence time of road salt in watersheds may be shorter than previously anticipated. Conversely, if climate becomes drier, with increased evapotranspiration, reduced infiltration and baseflow discharge may prolong salt storage, which could exacerbate biotic stresses from high chloride concentrations in streams.

AGU Fall Meeting Abstracts, Dec 1, 2019

Geochimica et Cosmochimica Acta, 2021

Abstract The Mg/Ca ratio of the infaunal benthic foraminifer Uvigerina peregrina is a commonly us... more Abstract The Mg/Ca ratio of the infaunal benthic foraminifer Uvigerina peregrina is a commonly used proxy for reconstructing bottom water paleotemperatures because it is hypothesized to be insensitive to changes in bottom water carbonate chemistry. This study presents core-top U. peregrina samples from the southwest Pacific from 0.6 to 4.4 km water depth, corresponding to water temperatures of 1–9 °C. Samples from New Zealand’s Bay of Plenty and Chatham Rise were compared to previous calibrations to assess Mg/Ca temperature sensitivity. Published core-top temperature sensitivies can explain U. peregrina Mg/Ca at a majority of our study sites, with the exception of sites at intermediate depths of ~2.4–3.3 km, where the Mg/Ca ratios are substantially higher than expected from these calibrations, possibly reflecting diagenetic or non-thermal effects. Stable isotope measurements (δ18O and δ13C), laser ablation analyses, and scanning electron microscope imagery complement trace element measurements to assess variables potentially affecting U. peregrina Mg/Ca at these sites. Morphotype variability, contamination, dissolution, and recrystallization all failed to provide satisfactory explanations for anomalously high Mg/Ca observations. We infer that a non-temperature control, perhaps related to carbonate chemistry, may be affecting the Mg incorporation in some U. peregrina specimens, though no factor has yet been clearly identified. It is unclear whether the factor affecting these sites is constant through time or could vary. For this reason, we recommend that Mg/Ca of recent specimens at each core site should be checked against established calibration curves prior to pursuing down-core paleotemperature reconstructions using U. peregrina. Where possible, paleotemperature estimates should also be validated using other independent proxies. Existing core-top calibrations effectively predict U. peregrina Mg/Ca at the majority of our study sites, but our findings underscore the need for a more thorough understanding of non-temperature factors that can influence Mg/Ca in U. peregrina.

Climate conditions in the Weddell Sea during the Pleistocene can be inferred by examining the abu... more Climate conditions in the Weddell Sea during the Pleistocene can be inferred by examining the abundance of foraminifer species and mineral fragments in ocean sediment cores. In particular, Neogloboquadrina incompta is a useful temperature proxy, and the abundance of terrigenous sediments is an indication of ice rafting. Using percent abundances enables correlation with other climate studies and with a global δ18O isotope stack. The proxies examined indicate at least four oscillations between cold and warm conditions related to global glacial and interglacial stages between 950 and 450 kya, with associated shifts in sea ice extent and deep-water formation. ! !

Water, Air, & Soil Pollution, 2017

Salt applied to roads for de-icing can persist for decades in watersheds, and understanding rates... more Salt applied to roads for de-icing can persist for decades in watersheds, and understanding rates of salt accumulation and export is important for anticipating the magnitude and duration of its environmental impacts. Salt removal is affected by storm frequency and intensity, both of which are projected to change as a result of anthropogenic climate change. To examine the potential outcomes of changing storm regimes on rates of salt export from watersheds, we studied chloride concentrations in baseflow and surface runoff in 5 years of streamflow data (taken at 20-min intervals) in a headwater tributary of the Hudson River. Baseflow, with chloride concentrations of 200–230 mg/L year-round, dominated streamflow, except during and after large storms, and accounted for about 90% of chloride export from the watershed. Extreme precipitation events (e.g., tropical storms) increased salt export mainly by increasing baseflow discharge, which remained elevated long after storms ended. While intense events accomplished more salt export per storm, they did not produce disproportionately higher export per volume of precipitation, compared to smaller rain events. Chloride export in a wet year was almost twice that in a dry year, despite less than a doubling of rainfall. Under future climate conditions, if winter precipitation shifts toward a higher proportion of rainfall, or summers experience a greater frequency of tropical storms, then long-term residence time of road salt in watersheds may be shorter than previously anticipated. Conversely, if climate becomes drier, with increased evapotranspiration, reduced infiltration and baseflow discharge may prolong salt storage, which could exacerbate biotic stresses from high chloride concentrations in streams.

Water Air and Soil Pollution, Sep 1, 2017

Salt applied to roads for de-icing can persist for decades in watersheds, and understanding rates... more Salt applied to roads for de-icing can persist for decades in watersheds, and understanding rates of salt accumulation and export is important for anticipating the magnitude and duration of its environmental impacts. Salt removal is affected by storm frequency and intensity, both of which are projected to change as a result of anthropogenic climate change. To examine the potential outcomes of changing storm regimes on rates of salt export from watersheds, we studied chloride concentrations in baseflow and surface runoff in 5 years of streamflow data (taken at 20-min intervals) in a headwater tributary of the Hudson River. Baseflow, with chloride concentrations of 200–230 mg/L year-round, dominated streamflow, except during and after large storms, and accounted for about 90% of chloride export from the watershed. Extreme precipitation events (e.g., tropical storms) increased salt export mainly by increasing baseflow discharge, which remained elevated long after storms ended. While intense events accomplished more salt export per storm, they did not produce disproportionately higher export per volume of precipitation, compared to smaller rain events. Chloride export in a wet year was almost twice that in a dry year, despite less than a doubling of rainfall. Under future climate conditions, if winter precipitation shifts toward a higher proportion of rainfall, or summers experience a greater frequency of tropical storms, then long-term residence time of road salt in watersheds may be shorter than previously anticipated. Conversely, if climate becomes drier, with increased evapotranspiration, reduced infiltration and baseflow discharge may prolong salt storage, which could exacerbate biotic stresses from high chloride concentrations in streams.

AGU Fall Meeting Abstracts, Dec 1, 2019

Geochimica et Cosmochimica Acta, 2021

Abstract The Mg/Ca ratio of the infaunal benthic foraminifer Uvigerina peregrina is a commonly us... more Abstract The Mg/Ca ratio of the infaunal benthic foraminifer Uvigerina peregrina is a commonly used proxy for reconstructing bottom water paleotemperatures because it is hypothesized to be insensitive to changes in bottom water carbonate chemistry. This study presents core-top U. peregrina samples from the southwest Pacific from 0.6 to 4.4 km water depth, corresponding to water temperatures of 1–9 °C. Samples from New Zealand’s Bay of Plenty and Chatham Rise were compared to previous calibrations to assess Mg/Ca temperature sensitivity. Published core-top temperature sensitivies can explain U. peregrina Mg/Ca at a majority of our study sites, with the exception of sites at intermediate depths of ~2.4–3.3 km, where the Mg/Ca ratios are substantially higher than expected from these calibrations, possibly reflecting diagenetic or non-thermal effects. Stable isotope measurements (δ18O and δ13C), laser ablation analyses, and scanning electron microscope imagery complement trace element measurements to assess variables potentially affecting U. peregrina Mg/Ca at these sites. Morphotype variability, contamination, dissolution, and recrystallization all failed to provide satisfactory explanations for anomalously high Mg/Ca observations. We infer that a non-temperature control, perhaps related to carbonate chemistry, may be affecting the Mg incorporation in some U. peregrina specimens, though no factor has yet been clearly identified. It is unclear whether the factor affecting these sites is constant through time or could vary. For this reason, we recommend that Mg/Ca of recent specimens at each core site should be checked against established calibration curves prior to pursuing down-core paleotemperature reconstructions using U. peregrina. Where possible, paleotemperature estimates should also be validated using other independent proxies. Existing core-top calibrations effectively predict U. peregrina Mg/Ca at the majority of our study sites, but our findings underscore the need for a more thorough understanding of non-temperature factors that can influence Mg/Ca in U. peregrina.

Climate conditions in the Weddell Sea during the Pleistocene can be inferred by examining the abu... more Climate conditions in the Weddell Sea during the Pleistocene can be inferred by examining the abundance of foraminifer species and mineral fragments in ocean sediment cores. In particular, Neogloboquadrina incompta is a useful temperature proxy, and the abundance of terrigenous sediments is an indication of ice rafting. Using percent abundances enables correlation with other climate studies and with a global δ18O isotope stack. The proxies examined indicate at least four oscillations between cold and warm conditions related to global glacial and interglacial stages between 950 and 450 kya, with associated shifts in sea ice extent and deep-water formation. ! !

Water, Air, & Soil Pollution, 2017

Salt applied to roads for de-icing can persist for decades in watersheds, and understanding rates... more Salt applied to roads for de-icing can persist for decades in watersheds, and understanding rates of salt accumulation and export is important for anticipating the magnitude and duration of its environmental impacts. Salt removal is affected by storm frequency and intensity, both of which are projected to change as a result of anthropogenic climate change. To examine the potential outcomes of changing storm regimes on rates of salt export from watersheds, we studied chloride concentrations in baseflow and surface runoff in 5 years of streamflow data (taken at 20-min intervals) in a headwater tributary of the Hudson River. Baseflow, with chloride concentrations of 200–230 mg/L year-round, dominated streamflow, except during and after large storms, and accounted for about 90% of chloride export from the watershed. Extreme precipitation events (e.g., tropical storms) increased salt export mainly by increasing baseflow discharge, which remained elevated long after storms ended. While intense events accomplished more salt export per storm, they did not produce disproportionately higher export per volume of precipitation, compared to smaller rain events. Chloride export in a wet year was almost twice that in a dry year, despite less than a doubling of rainfall. Under future climate conditions, if winter precipitation shifts toward a higher proportion of rainfall, or summers experience a greater frequency of tropical storms, then long-term residence time of road salt in watersheds may be shorter than previously anticipated. Conversely, if climate becomes drier, with increased evapotranspiration, reduced infiltration and baseflow discharge may prolong salt storage, which could exacerbate biotic stresses from high chloride concentrations in streams.