Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

Abstract

a b s t r a c tWe present a new method that quantifies the oxygen isotope geochemistry of Laurentide ice-sheet (LIS) meltwater across the last deglaciation, and reconstruct decadal-scale variations in the d 18 O of LIS meltwater entering the Gulf of Mexico between~18 and 11 ka. We employ a technique that combines laser ablation ICP-MS (LA-ICP-MS) and oxygen isotope analyses on individual shells of the planktic values of Mississippi River discharge from discrete core intervals range from À22‰ to À38‰ VSMOW. These values suggest a dynamic melting history of different parts of the LIS, with potential contributions to Mississippi River outflow from both the low-elevation, southern margin of the LIS and high-elevation, high-latitude domes in the LIS interior that were transported to the ablation zone. Prior to~15.5 ka, the d 18 O water value of the Mississippi River was similar to that of regional precipitation or low-latitude LIS meltwater, but the Ba concentration in the Mississippi basin was affected by changes in weathering within the watershed, complicating Ba-salinity relationships in the Gulf of Mexico. After 13 ka, our data suggest Mississippi River outflow did not influence surface salinity above our Gulf of Mexico Orca Basin core site. Rather, we hypothesize that open ocean conditions prevailed as sea level rose and the paleoshoreline at the southern edge of North America retreated northward.

Assessing the Spatial Origin of Meltwater Pulse 1A Using Oxygen‐Isotope Fingerprinting

“…In this study we did not assess a potential meltwater input into the Arctic, the Gulf of Mexico, or the North Pacific, even though there is some evidence of meltwater discharge into these regions. For example, paleoproxy records from the Gulf of Mexico have highlighted a significant δ 18 O decrease surrounding the time of MWP‐1A, thus suggesting that meltwater from the Laurentide ice sheet could have been routed toward the Gulf of Mexico instead of the North Altantic (Flower et al, ; Vetter et al, ). Planktic records from the Gulf of Alaska and the northwest Pacific also indicate meltwater addition during the broad period of MWP‐1A (Davies et al, ; Gorbarenko et al, ).…”

“…While only a few records suggest a sharp 18 O c drop as seen in our simulations during the ∼400 years of MWP-1A, the longer-term changes in the Southern Hemisphere are usually underestimated in our simulations, suggesting a continuous meltwater input over the period 14.6 to 13 ka BP. This model-data comparison thus indicates either that (i) the model is too sensitive to the meltwater input on centennial timescales; (ii) the paleoproxy records do not have the necessary resolution due to sedimentation rates or sampling interval to record the sharp change occurring during MWP-1A; (iii) the paleoproxy records are influenced by bioturbation or aliasing, such that if MWP-1A did produce a dramatic change in 18 O w or SST, the 18 O c record would have a less pronounced signal; (iv) meltwater was added to other regions, such as the Arctic (Poore et al, 1999), the Gulf of Mexico (Flower et al, 2004;Vetter et al, 2017), or the North Pacific; or (v) that meltwater was added over a longer time period.…”

LAtools: A data analysis package for the reproducible reduction of LA-ICPMS data

“…from Vetter et al (2017), and contains solely O. universa. Before analysis both sets of cultured specimens were oxidatively cleaned to remove residual organic material, and the fossil foraminifera were reductively cleaned to remove sedimentary contaminants, following standard protocols (e.g.…”

“…The spatial resolution of LA-ICPMS allows the targeted analysis of specific regions within a sample, and its minimally-destructive nature preserves the majority of the bulk sample, facilitating coupled analyses of a sample by different techniques (e.g. combined trace element and stable isotope analyses; Vetter et al, 2017). These capabilities have made LA-ICPMS popular across the Earth and Environmental Sciences, from geochemistry (Jackson et al, 2004;Burnham and Berry, 2017) to archaeology (Gratuze, 1999), biomineralization (Eggins et al, 2004;Spero et al, 2015) and paleoclimate research (Müller and Fietzke, 2016;Gothmann et al, 2015;Jochum et al, 2012).…”

Application of Individual Foraminifera Mg/Ca and δ18O Analyses for Paleoceanographic Reconstructions in Active Depositional Environments

“…Although Mg/Ca and δ 18 O are commonly measured in bulk samples (10-100 shells pooled per measurement) to provide mean hydrographic conditions (Anand et al, 2003;Elderfield & Ganssen, 2000;Shackleton, 1974), analyzing individual foraminifera shells may provide information about condition variations. This approach has been used on modern material from core-top sediment samples in areas with distinct seasonal contrast (Groeneveld et al, 2019;Wit et al, 2010) and over different time periods (Billups & Spero, 1996;Ford et al, 2015;Ganssen et al, 2011;Vetter et al, 2017) to reconstruct mean conditions and seasonal variability.…”