Taphonomic and Sedimentologic Study of the Cretaceous Tepee Buttes Limestone

The Tepee Buttes methane seep deposits exist today as topographically defined limestone features in the surrounding Pierre Shale of the Campanian Western Interior Seaway. The present sloping surface has previously been assumed to be indicative of original seep structure, and biofacies were interpreted as roughly ringing a central vent core. Contradictory field observations in this study have prompted a more detailed taphonomic approach to the Tepee Buttes limestone, and certain depositional features such as reworked horizontal shell beds were noted and examined in detail for the first time. The results of a taphonomic and sedimentologic analysis reveal a complex history of reworking that likely involved current action and bioturbation by burrowing seep fauna. We found no clear evidence for deposition along a sloping surface as inclined as today, and buttes are interpreted as having low/uneven original relief

Diet of the prehistoric population of Rapa Nui (Easter Island, Chile) shows environmental adaptation and resilience

Objectives: The Rapa Nui “ecocide” narrative questions whether the prehistoric population caused an avoidable ecological disaster through rapid deforestation and over-exploitation of natural resources. The objective of this study was to characterize prehistoric human diets to shed light on human adaptability and land use in an island environment with limited resources. Materials and methods: Materials for this study included human, faunal, and botanical remains from the archaeological sites Anakena and Ahu Tepeu on Rapa Nui, dating from c. 1400 AD to the historic period, and modern reference material. We used bulk carbon and nitrogen isotope analy- ses and amino acid compound specific isotope analyses (AA-CSIA) of collagen isolated from prehistoric human and faunal bone, to assess the use of marine versus terrestrial resources and to investigate the underlying baseline values. Similar isotope analyses of archaeological and modern botanical and marine samples were used to characterize the local environment. Results: Results of carbon and nitrogen AA-CSIA independently show that around half the protein in diets from the humans measured came from marine sources; markedly higher than previous estimates. We also observed higher d15N values in human collagen than could be expected from the local environment. Discussion: Our results suggest highly elevated d15N values could only have come from consump- tion of crops grown in substantially manipulated soils. These findings strongly suggest that the prehistoric population adapted and exhibited astute environmental awareness in a harsh environ- ment with nutrient poor soils. Our results also have implications for evaluating marine reservoir corrections of radiocarbon dates

Mercury Cycling in the North Pacific Subtropical Gyre as Revealed by Mercury Stable Isotope Ratios

The oceans are an important global reservoir for mercury (Hg), and marine fish consumption is the dominant human exposure pathway for its toxic methylated form. A more thorough understanding of the global biogeochemical cycle of Hg requires additional information on the mechanisms that control Hg cycling in pelagic marine waters. In this study, Hg isotope ratios and total Hg concentrations are used to explore Hg biogeochemistry in oligotrophic marine environments north of Hawaii. We present the first measurements of the vertical water column distribution of Hg concentrations and the Hg isotopic composition in precipitation, marine particles, and zooplankton near Station ALOHA (22°45′N, 158°W). Our results reveal production and demethylation of methylmercury in both the euphotic (0–175 m) and mesopelagic zones (200–1,000 m). We document a strong relationship between Hg isotopic composition and depth in particles, zooplankton, and fish in the water column and diurnal variations in Δ199Hg values in zooplankton sampled near the surface (25 m). Based on these observations and stable Hg isotope relationships in the marine food web, we suggest that the Hg found in large pelagic fish at Station ALOHA was originally deposited largely by precipitation, transformed into methyl‐Hg, and bioaccumulated in situ in the water column. Our results highlight how Hg isotopic compositions reflect abiotic and biotic production and degradation of methyl‐Hg throughout the water column and the importance of particles and zooplankton in the vertical transport of Hg

Mercury Cycling in the North Pacific Subtropical Gyre as Revealed by Mercury Stable Isotope Ratios

The oceans are an important global reservoir for mercury (Hg), and marine fish consumption is the dominant human exposure pathway for its toxic methylated form. A more thorough understanding of the global biogeochemical cycle of Hg requires additional information on the mechanisms that control Hg cycling in pelagic marine waters. In this study, Hg isotope ratios and total Hg concentrations are used to explore Hg biogeochemistry in oligotrophic marine environments north of Hawaii. We present the first measurements of the vertical water column distribution of Hg concentrations and the Hg isotopic composition in precipitation, marine particles, and zooplankton near Station ALOHA (22°45â ²N, 158°W). Our results reveal production and demethylation of methylmercury in both the euphotic (0â 175 m) and mesopelagic zones (200â 1,000 m). We document a strong relationship between Hg isotopic composition and depth in particles, zooplankton, and fish in the water column and diurnal variations in Î 199Hg values in zooplankton sampled near the surface (25 m). Based on these observations and stable Hg isotope relationships in the marine food web, we suggest that the Hg found in large pelagic fish at Station ALOHA was originally deposited largely by precipitation, transformed into methylâ Hg, and bioaccumulated in situ in the water column. Our results highlight how Hg isotopic compositions reflect abiotic and biotic production and degradation of methylâ Hg throughout the water column and the importance of particles and zooplankton in the vertical transport of Hg.Key PointsMMHg bioaccumulated in fish is derived primarily from Hg (II) deposited in atmospheric precipitationMarine particles host the majority of Hg available for production of MMHg in the open oceanMethylation and demethylation of Hg occurs throughout the euphotic and mesopelagic zones in the North Pacific Subtropical GyrePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150543/1/gbc20883.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150543/2/gbc20883_am.pd

EXPORTS Measurements and Protocols for the NE Pacific Campaign

EXport Processes in the Ocean from Remote Sensing (EXPORTS) is a large-scale NASA-led and NSF co-funded field campaign that will provide critical information for quantifying the export and fate of upper ocean net primary production (NPP) using satellite information and state of the art technology

Compound-Specific Isotope Geochemistry in the Ocean

Compound-specific isotope analysis encompasses a variety of methods for examining the naturally occurring isotope ratios of individual organic molecules. In marine environments, these methods have revealed heterogeneous sources and alteration processes that underlie the more commonly measured isotope ratios of bulk materials, as well as revealing signatures of marine metabolisms that may otherwise be impossible to isolate. Recently, compound-specific isotopic techniques have improved the reconstruction of metazoan diets and revealed a new potential of metazoan biomass as an archive of paleoecological information. Despite six decades of practice and a diversity of applications, the use of compound-specific isotopic techniques remains uncommon in marine studies. This review examines broad theoretical motivations behind compound-specific isotopic approaches, some applications to studies of marine carbon cycling and trophic relationships, and methodological limitations. In coming years, improvements in analytical efficiency and molecular or intramolecular specificity may transform compound-specific isotope analysis into a tool that can be applied more broadly and help to build global oceanographic data sets

Size fractionated zooplankton C:N, d13C, and d15N from the EXPORTS cruise on R/V Roger Revelle (RR1813) during August and September 2018

Dataset: Size Fractionated Zooplankton Carbon and NitrogenSize fractionated zooplankton C:N, d13C, and d15N from the EXPORTS cruise on R/V Roger Revelle (RR1813) during August and September 2018. Zooplankton were collected using a multiple opening-closing net and environmental sensing system (MOCNESS). For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/772776NSF Division of Ocean Sciences (NSF OCE) OCE-1830016, NSF Division of Ocean Sciences (NSF OCE) OCE-182942

Size fractionated zooplankton d13C and d15N of individual amino acids from EXPORTS cruise RR1813 in August 2018

Dataset: Zooplankton d13C and d15N of individual amino acidsThis dataset reports the size fractionated zooplankton d13C and d15N of individual amino acids from samples collected on the EXPORTS cruise (RR1813) in August 2018. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/868193NSF Division of Ocean Sciences (NSF OCE) OCE-1830016, NSF Division of Ocean Sciences (NSF OCE) OCE-182942

Marine Particle Chemistry: Influence on Biogeochemical Cycles and Particle Export

Marine particles play a key role in the cycling of most elements in the ocean. Particles are typically operationally defined by their collection method and, therefore, span a wide size range, within which chemical properties and interactions may be heterogeneous. The 12 papers in this collection address the challenges associated with studying particles in the marine environment with new types of chemical measurements, broadened oceanographic surveys, and novel sampling, experimentation, and modeling methods. Together, this collection of papers helps to fill critical gaps in our knowledge of the role of particles and elements in marine biogeochemical cycles