Spatial and temporal variability in the δ18Ow and salinity compositions of Gulf of Maine coastal surface waters

Hydrographic variability and dynamics in the Gulf of Maine are examined through the investigation of δ18Ow and salinity properties of coastal surface waters. Data from Gulf of Maine waters sampled over a decade, from 2003 to 2015, including a suite of samples that were collected monthly from April 2014 to March 2015, are presented. These water samples fall on a mixing line between Maine River Water (MRW) and Scotian Shelf Water (SSW). However, slope waters likely also contribute to these surface waters. The seasonal variability in water samples collected during 2014 and 2015 indicates the strong influence of river runoff on coastal Gulf of Maine surface water properties. The coastal surface Gulf of Maine mixing line presented in this paper is a needed baseline for reconstructing hydrographic variability in bicarbonates using oxygen isotopes

A Late Holocene Reconstruction of Ocean Climate Variability in the Gulf of Maine, USA, Based on Calibrated Isotope Records and Growth Histories from the Long-lived Ocean Quahog (Arctica islandica L.)

Understanding regional patterns of interannual to decadal-scale climate variability over the past 1000 years is critical for evaluating recently observed trends in atmosphere/ocean conditions, particularly in highly-productive ecosystems such as the Gulf of Maine (GOM) that are sensitive to minor changes in climate and/or changes in slope water input. To develop quantitative relationships between bivalve shell chemistry (d18Oc) and growing conditions, aquaculture-based experiments were developed using Mytilus edulis collected in the GOM and Greenland. These experiments yielded a highly accurate and precise paleothermometer [e.g., T °C = 16.28 (± 0.10) - 4.57 (± 0.15) {d18Oc VPBD – d18Ow VSMOW} + 0.06 (± 0.06) {d18Oc VPBD – d 18Ow VSMOW}2; r2 = 0.99; N= 323; p \u3c 0.0001] for M. edulis, and the techniques were applied to the long-lived bivalve species Arctica islandica. To examine ocean variability in the Western GOM during the last millennium, a 142-year-old living A. islandica and three fossil A. islandica shells (corrected 14CAMS = 1030 ± 78 AD; 1320 ± 45 AD; 1357 ± 40 AD) were collected for d18O and growth increment analysis. The standardized annual growth index (SGI) of the modern shell is significantly correlated with continuous GOM plankton recorder data (1961 – 2003; Calanus finmarchicus; r2 = 0.55; p \u3c 0.0001), and SGIs during the late Holocene contain significant periods of 2-6 years, suggesting that slope water variability coupled with North Atlantic Oscillation (NAO) dynamics is primarily responsible for productivity variability. Mean shell-derived isotopic changes were + 0.47 ‰ from 1000 AD to present, and likely reflect a 2 °C cooling caused by an increase in Labrador Current (LC) transport of ~ 0.7 Sv (1 Sv = 106 m3 s-1) and a corresponding decrease in Gulf Stream influence on GOM water temperatures during the past millennium. This hypothesis is consistent with modern observational relationships among the LC, GOM water temperatures, NAO, and Atlantic Multi-Decadal Oscillation (AMO). These results corroborate recent evidence of a large-scale cooling of slope waters and/or dynamical oceanographic changes outside the GOM during the Holocene, and suggest that a direct link exists between the GOM and Northwestern Atlantic

A Late Holocene Reconstruction of Ocean Climate Variability in the Gulf of Maine, USA, Based on Calibrated Isotope Records and Growth Histories from the Long-lived Ocean Quahog (Arctica islandica L.)

Understanding regional patterns of interannual to decadal-scale climate variability over the past 1000 years is critical for evaluating recently observed trends in atmosphere/ocean conditions, particularly in highly-productive ecosystems such as the Gulf of Maine (GOM) that are sensitive to minor changes in climate and/or changes in slope water input. To develop quantitative relationships between bivalve shell chemistry (d18Oc) and growing conditions, aquaculture-based experiments were developed using Mytilus edulis collected in the GOM and Greenland. These experiments yielded a highly accurate and precise paleothermometer [e.g., T °C = 16.28 (± 0.10) - 4.57 (± 0.15) {d18Oc VPBD – d18Ow VSMOW} + 0.06 (± 0.06) {d18Oc VPBD – d 18Ow VSMOW}2; r2 = 0.99; N= 323; p \u3c 0.0001] for M. edulis, and the techniques were applied to the long-lived bivalve species Arctica islandica. To examine ocean variability in the Western GOM during the last millennium, a 142-year-old living A. islandica and three fossil A. islandica shells (corrected 14CAMS = 1030 ± 78 AD; 1320 ± 45 AD; 1357 ± 40 AD) were collected for d18O and growth increment analysis. The standardized annual growth index (SGI) of the modern shell is significantly correlated with continuous GOM plankton recorder data (1961 – 2003; Calanus finmarchicus; r2 = 0.55; p \u3c 0.0001), and SGIs during the late Holocene contain significant periods of 2-6 years, suggesting that slope water variability coupled with North Atlantic Oscillation (NAO) dynamics is primarily responsible for productivity variability. Mean shell-derived isotopic changes were + 0.47 ‰ from 1000 AD to present, and likely reflect a 2 °C cooling caused by an increase in Labrador Current (LC) transport of ~ 0.7 Sv (1 Sv = 106 m3 s-1) and a corresponding decrease in Gulf Stream influence on GOM water temperatures during the past millennium. This hypothesis is consistent with modern observational relationships among the LC, GOM water temperatures, NAO, and Atlantic Multi-Decadal Oscillation (AMO). These results corroborate recent evidence of a large-scale cooling of slope waters and/or dynamical oceanographic changes outside the GOM during the Holocene, and suggest that a direct link exists between the GOM and Northwestern Atlantic

Hydroclimate variability from western Iberia (Portugal) during the Holocene: insights from a composite stalagmite isotope record

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Thatcher, D. L., Wanamaker, A. D., Denniston, R. F., Asmerom, Y., Polyak, V. J., Fullick, D., Ummenhofer, C. C., Gillikin, D. P., & Haws, J. A. Hydroclimate variability from western Iberia (Portugal) during the Holocene: insights from a composite stalagmite isotope record. Holocene, (2020): 095968362090864, doi:10.1177/0959683620908648.Iberia is predicted under future warming scenarios to be increasingly impacted by drought. While it is known that this region has experienced multiple intervals of enhanced aridity over the Holocene, additional hydroclimate-sensitive records from Iberia are necessary to place current and future drying into a broader perspective. Toward that end, we present a multi-proxy composite record from six well-dated and overlapping speleothems from Buraca Gloriosa (BG) cave, located in western Portugal. The coherence between the six stalagmites in this composite stalagmite record illustrates that climate (not in-cave processes) impacts speleothem isotopic values. This record provides the first high-resolution, precisely dated, terrestrial record of Holocene hydroclimate from west-central Iberia. The BG record reveals that aridity in western Portugal increased secularly from 9.0 ka BP to present, as evidenced by rising values of both carbon (δ13C) and oxygen (δ18O) stable isotope values. This trend tracks the decrease in Northern Hemisphere summer insolation and parallels Iberian margin sea surface temperatures (SST). The increased aridity over the Holocene is consistent with changes in Hadley Circulation and a southward migration of the Intertropical Convergence Zone (ITCZ). Centennial-scale shifts in hydroclimate are coincident with changes in total solar irradiance (TSI) after 4 ka BP. Several major drying events are evident, the most prominent of which was centered around 4.2 ka BP, a feature also noted in other Iberian climate records and coinciding with well-documented regional cultural shifts. Substantially, wetter conditions occurred from 0.8 ka BP to 0.15 ka BP, including much of the ‘Little Ice Age’. This was followed by increasing aridity toward present day. This composite stalagmite proxy record complements oceanic records from coastal Iberia, lacustrine records from inland Iberia, and speleothem records from both northern and southern Spain and depicts the spatial and temporal variability in hydroclimate in Iberia.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported, in part, by the US National Science Foundation (Grants: #1804528 to ADW; #1804635 to RD; #1804132 to CCU; #1806025 to YA and VP; #1805163 to DPG; BCS-0455145, BCS-0612923, and BCS-1118155 to JAH)

Life histories and niche dynamics in late Quaternary proboscideans from Midwestern North America: evidence from stable isotope analyses

Stable isotopes of mammoths and mastodons have the potential to illuminate ecological changes in late Pleistocene landscapes and megafaunal populations as these species approached extinction. The ecological factors at play in this extinction remain unresolved, but isotopes of bone collagen (δ13C, δ15N) and tooth enamel (δ13C, δ18O, 87Sr/86Sr) from the Midwest, USA are leveraged to examine ecological and behavioral changes that occurred during the last interglacial-glacial cycle. Both species had significant C3 contributions to their diets and experienced increasing levels of niche overlap as they approached extinction. A subset of mastodons after the last glacial maximum (LGM) exhibit low δ15N values that may represent expansion into a novel ecological niche, perhaps densely occupied by other herbivores. Stable isotopes from serial and micro-sampled enamel show increasing seasonality and decreasing temperatures as mammoths transitioned from Marine Isotope Stage (MIS) 5e to glacial conditions (MIS 4, MIS 3, MIS 2). Isotopic variability in enamel suggests mobility patterns and life histories have potentially large impacts on the interpretation of their stable isotope ecology. This study further refines the ecology of midwestern mammoths and mastodons demonstrating increasing seasonality and niche overlap as they responded to landscape changes in the final millennia before extinction

Unexpected isotopic variability in biogenic aragonite: A user issue or proxy problem?

The present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive, the marine bivalve Arctica islandica, with an emphasis on the potential of human-induced variability arising from sampling techniques. Stable carbon (d13Ccarbonate) and oxygen (d18Ocarbonate) isotopes were analyzed for split (intra-sample) and replicate (intra- and inter-shell) samples taken from a group of laboratory-reared individuals, a natural population from northern Norway, and a natural population from the Gulf of Maine, USA. Compared to analytical uncertainty of 0.17 ‰ and 0.30 ‰ for d13C and d18O, respectively, among the natural populations, the mean difference between shell splits and shell replicates ranged from 0.12 ‰ and 0.33 ‰ for d13C and d18O, respectively. Our data suggest that heterogeneity of the carbonate material (i.e., large range of isotopic composition within one sample due to seasonal environmental variability) may contribute to “unexpected” variability more than human-induced error from sampling imprecision when collecting whole annual increments. Furthermore, d13C from juvenile shells were highly variable (2s standard deviation = 0.65 ‰), approximately four times more variable than analytical precision. High precision among d18O measurements of the laboratory-reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater. Monte Carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication. Substantial reduction in uncertainty occurs when increasing from two to three shells, however replication using a total of four shells further decreased uncertainty to within the 99% confidence level. Published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual. Oftentimes, however, isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error. Our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy-derived noise. Furthermore, population-specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series

Reply to Nott: Assessing biases in speleothem records of flood events

This article is published as Denniston, Rhawn F., Gabriele Villarini, Angelique N. Gonzales, Victor J. Polyak, Caroline C. Ummenhofer, Matthew S. Lachniet, Alan D. Wanamaker Jr, William F. Humphreys, David Woods, and John Cugley. "Reply to Nott: Assessing biases in speleothem records of flood events." Proceedings of the National Academy of Sciences of the United States of America 112, no. 34 (2015): E4637. doi: 10.1073/pnas.1513354112. Posted with permission.</p

Environmental controls on the boron and strontium isotopic composition of aragonite shell material of cultured Arctica islandica

Ocean acidification, the decrease in ocean pH associated with increasing atmospheric CO2, is likely to impact marine organisms, particularly those that produce carbonate skeletons or shells. Therefore, it is important to investigate how environmental factors (seawater pH, temperature and salinity) influence the chemical compositions in biogenic carbonates. In this study we report the first high-resolution strontium (Sr-87 / Sr-86 and delta(88) / Sr-86) and boron (delta B-11) isotopic values in the aragonite shell of cultured Arctica islandica (A. islandica). The Sr-87/Sr-86 ratios from both tank water and shell samples show ratios nearly identical to the open ocean, which suggests that the shell material reflects ambient ocean chemistry without terrestrial influence. The Sr-84-Sr-87 double-spike-resolved shell delta(88) / Sr-86 and Sr concentration data show no resolvable change throughout the culture period and reflect no theoretical kinetic mass fractionation throughout the experiment despite a temperature change of more than 15 degrees C. The delta B-11 records from the experiment show at least a 5% increase through the 29-week culture season (January 2010-August 2010), with low values from the beginning to week 19 and higher values thereafter. The larger range in delta B-11 in this experiment compared to predictions based on other carbonate organisms (2-3 %) suggests that a species-specific fractionation factor may be required. A significant correlation between the Delta pH (pH(shell) - pH(sw)) and seawater pH (pH(sw)) was observed (R-2 = 0.35), where the pH(shell) is the calcification pH of the shell calculated from boron isotopic composition. This negative correlation suggests that A. islandica partly regulates the Delta pH of the extrapallial fluid. However, this proposed mechanism only explains approximately 35% of the variance in the delta B-11 data. Instead, a rapid rise in delta B-11 of the shell material after week 19, during the summer, suggests that the boron uptake changes when a thermal threshold of \u3e 13 degrees C is reached