Natural Variability of Skeletal Elemental Phosphorus (P/Ca), Lead (Pb/Ca), and Barium (Ba/Ca) in the Western Pacific Sclerosponges Acanthoceatetes wellsi and Astrosclera welleyana

Abstract Elemental proxies are used to reconstruct oceanic conditions that predate modern records. Such proxies have been established in corals, but few attempts have been made in sclerosponges. However, their wide distribution and slow growth make sclerosponges good candidates for multicentury recorders of local oceanographic conditions. Here, we investigated the elements P, Pb, and Ba (standardized to Ca) in the accretionary skeleton of two sclerosponge species, Acanthocheatetes wellsi (high‐Mg calcite) collected from Palau and Saipan, and Astrosclera willeyana (aragonite) collected in Saipan. All specimens were stained in situ and left to grow on the reef for two years. We measured these elements in (1) 2‐year bulk skeletal samples to explore the effect of local environmental conditions and mineralogy on the skeletal composition and (2) at high resolution to determine the temporal variability of these elements and evaluate their potential as paleo‐proxies. We found that for A. wellsi, bulk P/Ca was higher and Pb/Ca lower in Palau than in Saipan suggesting that these elements vary in response to the local seawater elemental composition. In Saipan, bulk P/Ca was higher in A. wellsi compared to A. willeyana, which is most likely due to differences in mineralogy. At high resolution, only P/Ca signatures appeared to be moderately reproducible within and among species suggesting that sclerosponges are recording seawater P/Ca. In Saipan, A. willeyana P/Ca variability also correlated with temperature suggesting that variation in seawater P concentrations co‐varied with temperature. Additional study is needed to determine if sclerosponge P/Ca is a reliable proxy of seawater nutrient variability

Boron isotopic geochemistry of the McMurdo Dry Valley lakes, Antarctica

The geochemistry of boron was investigated in the ice-covered lakes and glacier meltwater streams within Taylor and Wright Valley of the McMurdo Dry Valleys (MCM), Antarctica, in order to achieve a greater understanding of the source of boron to these aquatic systems and how in-lake processes control boron concentration. Selected lake depths (surface and bottom water) and streams were analyzed for boron geochemistry. Boron stable isotope values in these waters span the range of +12.3‰ to +51.4‰, which corresponds to the variations from glacier meltwater streams to the hypolimnion of a highly evaporated hypersaline lake. The data demonstrate that the major sources of B to the aquatic system are via terrestrial chemical weathering of aluminosilicates within the stream channels, and a marine source, either currently being introduced by marine-derived aerosols or in the form of ancient seawater. Lakes Fryxell, Hoare, and upper waters of Lake Joyce, which experience more terrestrial influence of aluminosilicate chemical weathering via glacial meltwater streams, display a mixture of these two major sources, while the source of B in the bottom waters of Lake Joyce appears to be primarily of marine origin. Lakes Bonney and Vanda and the Blood Falls brine have a marine-like source whose δ11B values have become more positive by mineral precipitation and/or adsorption. Don Juan Pond displays a terrestrial aluminosilicate influence of a marine-like source. These hypersaline lake waters from Antarctica are similar in δ11B to other hypersaline lake waters globally, suggesting that similar processes control their B geochemistry. © 2014 Elsevier B.V

Role of seafloor production versus continental basalt weathering in Middle to Late Ordovician seawater 87Sr/86Sr and climate

Highlights • Rise in Middle Ordovician global sea level suggests increased seafloor production. • Hydrothermal weathering drives inflection in marine strontium isotopes (87Sr/86Sr). • Oxygen isotope (O) data demonstrate cooling concurrent with 87Sr/86Sr inflection. • Continental silicate weathering can drive cooling. • Cooling from weathering can counteract volcanic carbon dioxide (CO2) degassing. The global climate of the Ordovician Period (486.9 to 443.1 Ma) is characterized by cooling that culminated in the Hirnantian glaciation. Chemical weathering of Ca- and Mg-bearing silicate minerals and the subsequent trapping of carbon in marine carbonates act as a sink for atmospheric CO2 on multi-million-year time scales, with basaltic rocks consuming CO2 at a greater rate than rocks of granitic composition. The oceanic Sr isotope ratio (87Sr/86Sr) can act as a geochemical proxy for the relative proportion of basaltic versus granitic weathering. Oxygen isotopes (O) act as a proxy for paleotemperature and ice volume, providing a useful complement to 87Sr/86Sr in studies of ancient climate. Previous studies have reported stepwise cooling (increasing O) during the Middle to Late Ordovician. Combined with Sr and C cycle models, this has led to the hypothesis that continental silicate weathering of mafic material drove Ordovician cooling (e.g., the Taconic Orogeny). However, Sr and C cycle models have not accounted for an apparent rise in sea level and seafloor production in the Middle Ordovician (Darriwilian), which would increase the hydrothermal Sr flux as well as degassing along continental volcanic arcs. Furthermore, some Ordovician studies contain temporal uncertainty between 87Sr/86Sr and O curves if they are not based on paired analyses, which can obscure the relationship between silicate weathering and cooling. Here, we present new paired 87Sr/86Sr and O data from conodont apatite and integrate this with both a deterministic (forward) and stochastic (reverse) modeling approach to argue that increased hydrothermal weathering played a role in driving marine 87Sr/86Sr, specifically an inflection occurring in the Pygoda serra conodont zone of the mid-Darriwilian Stage (∼ 460.9 Ma ± 1 My). This 87Sr/86Sr inflection is accompanied by an increase in O, consistent with climate cooling. Clarifying the role of seafloor production for marine 87Sr/86Sr and the implications for Ordovician cooling allows for a more nuanced understanding of the factors that drive multi-million-year shifts in climate

Experimental and field evaluation of otolith strontium as a marker to discriminate between river-spawning populations of walleye in Lake Erie

Otolith microchemistry is a commonly used tool for stock discrimination in fisheries management. Two key questions remain with respect to its effectiveness in discriminating among river-spawning populations. First, do larvae remain in their natal river long enough for their otoliths to pick up that systemâ s characteristic chemical signature? Second, are larval otolith microchemical differences between natal rivers sufficiently large to overcome spatiotemporal variation in water chemistry? We quantified how larval age, the ratio of ambient strontium to calcium concentrations (Sr:Ca), and water temperature influence otolith Sr in both lab-reared and wild-collected Lake Erie walleye (Sander vitreus). Otolith microchemistry shows promise as a spawning stock discrimination tool, given that otolith Sr in larval walleye: 1) is more strongly influenced by ambient Sr:Ca than by temperature; 2) reflects Sr:Ca levels in the natal environment, even in larvae as young as 2 d; and 3) can effectively discriminate between larvae captured in two key Lake Erie spawning tributaries, even in the face of short larval river-residence times and within-year and across-year variation in ambient Sr:Ca.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Boron isotopic geochemistry of the McMurdo Dry Valley lakes, Antarctica

The geochemistry of boron was investigated in the ice-covered lakes and glacier meltwater streams within Taylor and Wright Valley of the McMurdo Dry Valleys (MCM), Antarctica, in order to achieve a greater understanding of the source of boron to these aquatic systems and how in-lake processes control boron concentration. Selected lake depths (surface and bottom water) and streams were analyzed for boron geochemistry. Boron stable isotope values in these waters span the range of +12.3‰ to +51.4‰, which corresponds to the variations from glacier meltwater streams to the hypolimnion of a highly evaporated hypersaline lake. The data demonstrate that the major sources of B to the aquatic system are via terrestrial chemical weathering of aluminosilicates within the stream channels, and a marine source, either currently being introduced by marine-derived aerosols or in the form of ancient seawater. Lakes Fryxell, Hoare, and upper waters of Lake Joyce, which experience more terrestrial influence of aluminosilicate chemical weathering via glacial meltwater streams, display a mixture of these two major sources, while the source of B in the bottom waters of Lake Joyce appears to be primarily of marine origin. Lakes Bonney and Vanda and the Blood Falls brine have a marine-like source whose δ11B values have become more positive by mineral precipitation and/or adsorption. Don Juan Pond displays a terrestrial aluminosilicate influence of a marine-like source. These hypersaline lake waters from Antarctica are similar in δ11B to other hypersaline lake waters globally, suggesting that similar processes control their B geochemistry. © 2014 Elsevier B.V