skip to main content

The Antarctic scallop Adamussium colbecki may be a crucial paleoenvironmental proxy for coastal Antarctica. For example, two highly seasonal environmental parameters, glacial melt and productivity, were linked to trace elemental concentrations in a previous bulk shell analysis and a transect spanning ~ 3 months of juvenile growth. However, neither study examined seasonal variation in trace elements or tied variation to distances between small ridges (striae) on valve surfaces, which may also vary seasonally. Striae and interstrial growth between them are expressed as alternating narrow and wide groups (presumably winter and summer growth, respectively). If tied to trace elemental concentrations, striae could provide high-resolution sclerochronological proxies for seawater conditions. Here, we evaluate whether trace elements archived in A. colbecki striae can be used as seasonal indicators of glacial influence and nutrients over A. colbecki ontogeny. We examined trace elements from an adult and juvenile A. colbecki (shell height, 80.2 mm and 17.1 mm, respectively) collected live by divers from ~ 12 m water depth in Explorers Cove, western McMurdo Sound (2008 and 2016, respectively). Trace elements linked to glacial melt (Mg/Ca, Mn/Ca, Fe/Ca, and Pb/ Ca), metabolism (Mg/Ca), and productivity (Ba/Ca) were sampled with an LA-ICP-MS on each stria along the central growth axis of lower (right) valves from umbo to growing margin. Distances between sampled striae were measured along the central margin (FIJI). Interstrial distances (ISDs) and trace elements were compared using wavelet coherence analysis (Wavelet- Comp 1.1) and cross-correlation. Coherence and correlations that exceeded 95% significance are reported here. Coherence identifies areas of covariance between ISD and trace elements over ontogeny; cross-correlation describes the direction (±) of correlation between 113 NAPC 2019 PROGRAM & ABSTRACTS ISDs and trace elements where coherence exists. We expected trace elements that increase with glacial melt (Fe, Mn, Pb), productivity (Ba), and altered metabolism (Mg) to be coherent and correlate positively with ISD (highest concentrations at wide summer striae) throughout ontogeny. Preliminary results mostly do not conform to predictions. Though correlation remains consistently positive or negative under strong coherence, most elements are only coherent with ISD for short strial sequences (~ 8 striae) and only during adult growth. Of the elements associated with glacial melt, only Mn correlates positively with ISD and may be a potential proxy for seasonality. Other indicators of glacial melt (Pb/Ca, Fe/Ca) and productivity (Ba/Ca) correlate negatively with ISD. Mg/Ca correlates positively with ISD, indicating seasonal effects on metabolism. Ontogenetic variation in coherence urges cautious use of ISDs as proxies, but Pb/Ca (anthropogenic in Antarctica) is coherent with ISD throughout ontogeny; further analysis might illuminate seasonal effects of human activities on Antarctic ecosystems.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    Sea ice is critical in structuring Antarctic marine ecosystems, controlling disturbance and primary productivity. Sea ice either melts annually or persists for multiple years, but variability in sea-ice duration is poorly understood prior to satellite images. The Antarctic scallop Adamussium colbecki, with its circum-Antarctic distribution and Holocene fossil history, may be a proxy for sea-ice duration. Previous work on A. colbecki links some trace elements to ice melt and productivity. Further, increments between growth bands (striae) are thought to vary seasonally. To evaluate A. colbecki suitability as a sea-ice proxy, we tested correspondence between growth and trace elements known to represent sea ice or productivity at two sites in western McMurdo Sound: Explorers Cove (EC) with multiannual sea ice and Bay of Sails (BOS) with annual sea ice. Trace element signals should be dampened or absent at EC, whereas those from BOS should cycle annually. One A. colbecki shell each from EC and BOS were collected live in 12 m of water. Trace elements previously linked to ice melt (Mn/Ca, Fe/Ca, and Pb/Ca), metabolism (Mg/Ca), and primary productivity (Ba/Ca, Li/Ca) were sampled from interstrial increments using an LA-ICP-MS along the central axis from umbo to last striae. Interstrial distances (ISDs) were measured and compared to trace elements using wavelet coherence analysis. Coherence (covariance between ISD and trace elements) exceeding 95% significance are reported here. Results indicate that ISD and trace elements only cohere during episodic sea-ice melt at EC and cohere throughout adult growth at BOS. All EC trace element concentrations display a common pattern: cyclic growth followed minimal variation in early adult ontogeny, with intermittent variation resuming later in adult growth. In contrast, trace elements from the BOS scallop exhibit strong cyclic behavior throughout ontogeny. ISD coheres with trace elements at EC for short strial sequences (5-30) twice in adult growth, corresponding to partial sea ice melts at EC during 1999 and 2002. Conversely, BOS trace elements cohere with ISD for long (20-140) strial sequences during adult growth, indicating annual sea-ice melt. Results indicate that A. colbecki archives sea-ice duration, thus its fossil record can be used to investigate past variability. 
    more » « less
  2. null (Ed.)
    The Antarctic scallop Adamussium colbecki is a promising proxy for sea-ice persistence and can potentially resolve subannual seawater conditions characteristic of annual and multiannual sea ice. Alternating groups of widely- and narrowly-spaced striae (small ridges on valve surfaces) are thought to indicate seasonal growth differences: wide groups in summer, narrow groups in winter. Shell oxygen (δ18Os) and carbon (δ13Cs) in striae groups may therefore reflect seasonal seawater conditions. We expect lower δ18Os in wide summer striae groups under both annual and multiannual sea ice if glacial meltwater mixes through the water column. We also expect higher δ13Cs in wide striae groups under annual sea ice but not under multiannual sea ice, as phytoplankton blooms post seaice breakout enrich seawater δ13CDIC. Scallops were collected from two sites in western McMurdo Sound (Ross Sea) located ~30 km apart: Explorers Cove (EC) has multiannual sea ice and Bay of Sails (BOS) has annual sea ice. Adults were collected live by divers at 9–18 m depth in 2008 from EC and BOS. Additional juveniles (< 2 yrs) were collected from EC in 2016. Two adults each from EC and BOS and two 2016 juveniles were serially sampled for stable isotopes. δ13Cs decreases over ontogeny due to metabolic effects; the linear trend was removed to enable seasonal comparison. Detrended residuals are referred to as δ13Cs det. Mean δ18Os (~3.7‰) is not different in narrow and wide striae groups under either annual or multiannual sea ice, suggesting negligible glacial meltwater mixing at depth and minimal seasonal temperature change at both sites. δ18Os values are within expected equilibrium range and decrease over ontogeny, suggesting increased growth during warmer temperatures in older scallops. In contrast, mean δ13Cs det is ~1‰ higher in wide summer striae groups than narrow winter striae groups under annual sea ice at BOS, but not different between striae groups under multiannual sea ice in EC adults. δ13Cs det is also higher in wide summer striae groups from 2016 EC juveniles, however sea ice broke out at EC in 2015, so juveniles experienced annual-like sea-ice conditions. Seasonal differences in δ13Cs suggest that carbon isotopes coupled with striae width in A. colbecki may be a good proxy for sea-ice persistence in Antarctica both in modern and fossil assemblages. 
    more » « less
  3. In the southwestern United States, California (CA) is one of the most climatically sensitive regions given its low (≤250 mm/year) seasonal precipitation and its inherently variable hydroclimate, subject to large magnitude modulation. To reconstruct past climate change in CA, cave calcite deposits (stalagmites) have been utilized as an archive for environmentally sensitive proxies, such as stable isotope compositions (δ18O, δ13C) and trace element concentrations (e.g., Mg, Ba, Sr). Monitoring the cave and associated surface environments, the chemical evolution of cave drip-water, the calcite precipitated from the drip-water, and the response of these systems to seasonal variability in precipitation and temperature is imperative for interpreting stalagmite proxies. Here we present monitored drip-water and physical parameters at Lilburn Cave, Sequoia Kings Canyon National Park (Southern Sierra Nevada), CA, and measured trace element concentrations (Mg, Sr, Ba, Cu, Fe, Mn) and stable isotopic compositions (δ18O, δ2H) of drip-water and for calcite (δ18O) precipitated on glass substrates over a two-year period (November 2018 to February 2021) to better understand how chemical variability at this site is influenced by local and regional precipitation and temperature variability. Despite large variability in surface temperatures and precipitation amount and source region (North Pacific vs. subtropical Pacific), Lilburn Cave exhibits a constant cave environment year-round. At two of the three sites within the cave, drip-water δ18O and δ2H are influenced seasonally by evaporative enrichment. At a third collection site in the cave, the drip-water δ18O responds solely to precipitation δ18O variability. The Mg/Ca, Ba/Ca, and Sr/Ca ratios are seasonally responsive to prior calcite precipitation at all sites but minimally to water-rock interaction. Lastly, we examine the potential of trace metals (e.g., Mn2+and Cu2+as a geochemical proxy of recharge and find that variability in their concentrations has high potential to denote the onset of the rainy season in the study region. The drip-water composition is recorded in the calcite, demonstrating that stalagmites from Lilburn Cave, and potentially more regionally, could record seasonal variability in weather even during periods of substantially reduced rainfall.

    more » « less
  4. Otolith chemistry has gained increasing attention as a tool for analyzing various aspects of fish biology, such as stock dynamics, migration patterns, hypoxia and pollution exposure, and connectivity between habitats. While these studies often assume otolith elemental concentrations reflect environmental conditions, physiological processes are increasingly recognized as a modulating and/or controlling factor. In particular, biomineralization—the complex, enzyme-regulated construction of CaCO3 crystals scaffolded by proteins—is believed to play a critical role in governing otolith chemical patterns. This review aims to summarize the knowledge on otolith composition and biophysical drivers of biomineralization, present hypotheses on how biomineralization should affect element incorporation, and test the validity thereof with selected case studies. Tracers of environmental history are assumed to be dominated by elements that substitute for Ca during crystal growth or that occur randomly trapped within the crystal lattice. Strontium (Sr) and barium (Ba) largely comply with the biomineralization-based hypotheses that otolith element patterns reflect environmental concentrations, without additional effects of salinity, but can be influenced by physiological processes, typically exhibiting decreasing incorporation with increasing growth. Conversely, tracers of physiology are assumed to be elements under physiological control and primarily occur protein-bound in the otolith’s organic matrix. Physiological tracers are hypothesized to reflect feeding rate and/or growth, decrease with fish age, and exhibit minimal influence of environmental concentration. The candidate elements phosphorus (P), copper (Cu) and zinc (Zn) confirm these hypotheses. Magnesium (Mg) is believed to be randomly trapped in the crystal structure and hence a candidate for environmental reconstruction, but the response to all examined drivers suggest Mg to be coupled to growth. Manganese (Mn) substitutes for Ca, but is also a co-factor in matrix proteins, and therefore exhibits otolith patterns reflecting both environmental (concentration and salinity) and physiological (ontogeny and growth) histories. A consistent temperature response was not evident across studies for either environmental or physiological tracers, presumably attributable to variable relationships between temperature and fish behavior and physiology (e.g., feeding rate, reproduction). Biomineralization thus has a controlling effect on otolith element concentrations for elements that are linked with somatic growth, but not for elements that substitute for Ca in the crystal lattice. Interpretation of the ecological significance of patterns from field samples therefore needs to consider the impact of the underlying biomineralization processes of the element in question as well as physiological processes regulating the availability of ions for inclusion in the growing crystal lattice. Such understanding will enhance the utility of this technique to address fisheries management questions. 
    more » « less
  5. Abstract Mineral/melt partition coefficients have been widely used to provide insights into magmatic processes. Olivine is one of the most abundant and important minerals in the lunar mantle and mare basalts. Yet, no systematic olivine/melt partitioning data are available for lunar conditions. We report trace element partition data between host mineral olivine and its melt inclusions in lunar basalts. Equilibrium is evaluated using the Fe-Mg exchange coefficient, leading to the choice of melt inclusion-host olivine pairs in lunar basalts 12040, 12009, 15016, 15647, and 74235. Partition coefficients of 21 elements (Li, Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Y, Zr, Nb, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were measured. Except for Li, V, and Cr, these elements show no significant difference in olivine-melt partitioning compared to the data for terrestrial samples. The partition coefficient of Li between olivine and melt in some lunar basalts with low Mg# (Mg# < 0.75 in olivine, or < ~0.5 in melt) is higher than published data for terrestrial samples, which is attributed to the dependence of DLi on Mg# and the lack of literature DLi data with low Mg#. The partition coefficient of V in lunar basalts is measured to be 0.17 to 0.74, significantly higher than that in terrestrial basalts (0.003 to 0.21), which can be explained by the lower oxygen fugacity in lunar basalts. The significantly higher DV can explain why V is less enriched in evolved lunar basalts than terrestrial basalts. The partition coefficient of Cr between olivine and basalt melt in the Moon is 0.11 to 0.62, which is lower than those in terrestrial settings by a factor of ~2. This is surprising because previous authors showed that Cr partition coefficient is independent of fO2. A quasi-thermodynamically based model is developed to correlate Cr partition coefficient to olivine and melt composition and fO2. The lower Cr partition coefficient between olivine and basalt in the Moon can lead to more Cr enrichment in the lunar magma ocean, as well as more Cr enrichment in mantle-derived basalts in the Moon. Hence, even though Cr is typically a compatible element in terrestrial basalts, it is moderately incompatible in primitive lunar basalts, with a similar degree of incompatibility as V based on partition coefficients in this work, as also evidenced by the relatively constant V/Cr ratio of 0.039 ± 0.011 in lunar basalts. The confirmation of constant V/Cr ratio is important for constraining concentrations of Cr (slightly volatile and siderophile) and V (slightly siderophile) in the bulk silicate Moon. 
    more » « less