Papers by Dr. Leanne G Hancock
Palaeogeography, Palaeoclimatology, Palaeoecology, 2019
Deposition of the Miocene Monterey Formation into numerous basins provides an ideal opportunity t... more Deposition of the Miocene Monterey Formation into numerous basins provides an ideal opportunity to study how preservation of geochemical signatures varies within and among basins as a function of local and global climatic and oceanic conditions. This study presents commonly
employed redox indicators, including iron (Fe) speciation and redox-sensitive trace metal concentrations (Mo, U, V), to constrain paleoredox conditions from three Monterey locations: the Santa Barbara Basin, the Santa Maria Basin, and the San Joaquin Basin. The Fe speciation
geochemistry of the Santa Barbara and Santa Maria basin sediments are consistent with a wide range of redox conditions from suboxic to euxinic. These results, in combination with associated phosphorites and trace metal enrichment patterns, indicate oscillatory redox conditions, perhaps with a chemocline that fluctuated above the sediment-water interface on seasonal or multi-year timescales. Overall, these sections were deposited in environments similar to modern phosphorite-forming and upwelling-dominated oxygen minimum zone settings such as the Peru Margin. Geochemical evidence indicates that the San Joaquin Basin was generally more restricted and more stably anoxic compared to the other two basins, perhaps more analogous to the modern Cariaco Basin, at least for the studied interval. Iron speciation in the San Joaquin
Basin reveals anoxia and euxinia over the entirety of the studied interval, although trace metal concentrations are generally at the low end of those typical of anoxic/euxinic conditions—consistent with a restricted connection with the open ocean. The one exception is an interval c.
~11.6 million years ago (Ma) with elevated concentrations of redox-sensitive elements that may represent a decrease in basin restriction or an increase in water column sulfide concentrations. The present-day California Margin does not achieve euxinic conditions in similar basinal settings comparable with those of our Monterey sections, suggesting fundamental differences for the Miocene California margin that may carry implications for global-scale oxygen deficiency in Miocene oxygen minimum zones.
Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, ... more Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (D 47), as much as B0.2% lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings.
We review the ecology and fossil record of parasitic and suspected parasitic foraminifera. Nine s... more We review the ecology and fossil record of parasitic and suspected parasitic foraminifera. Nine species of foraminifera are known to be parasitic, obtaining nutrients from their host, and 13 are suspected parasites that require taxonomic and eco-logic work to document their trophic relationships. Roughly 0.22% and 0.32% of all benthic foraminifera are known or suspected parasites, respectively. Endo-and ectoparasites are most common, followed by kleptoparasites and putatively hermit endoparasites. While most diverse in the shallow-water tropics, the best-known foraminiferal parasites live in colder North Atlantic and Antarctic waters. Body size comparisons reveal patterns similar to parasitic metazoans: 1) a few parasitic foraminifera are larger than most benthic foraminifera and most are larger than their free-living relatives; 2) most are smaller than their metazoan hosts, but are roughly similar in size to protozoan hosts with one exception; and 3) larger parasitic foraminifera infest larger hosts, consistent with Harrison's rule. Ectoparasitic foraminifera also follow Harrison's rule, but endoparasites do not because they are spatially constrained by living within the host. Suspected foraminiferal parasites are first recorded from the Late Jurassic and parasitic foraminifera from the Early Cretaceous, while the majority evolved in the Cenozoic. Cretaceous Talpinella cunicularia has one of the longest known host-parasitic relationships of 18 Myr. Sixteen species bioerode their hosts, but only two trace fossils from parasitic foraminifera are known. Their abundance, broad geographic distribution and excellent fossil record make parasitic foraminifera and their hosts an excellent model to study how climate and environmental change affects intimately-associated species.
We studied the population dynamics and parasite load of the foraminifer Cibicides antarcti-cus on... more We studied the population dynamics and parasite load of the foraminifer Cibicides antarcti-cus on its host the Antarctic scallop Adamussium colbecki from three localities differing by sea ice cover within western McMurdo Sound, Ross Sea, Antarctica: Explorers Cove, Bay of Sails and Herbertson Glacier. We also estimated CaCO 3 biomass and annual production for both species. Cibicides populations varied by locality, valve type, and depth. Explorers Cove with multiannual sea ice had larger populations than the two annual sea ice localities, likely related to differences in nutrients. Populations were higher on Adamussium top valves, a surface that is elevated above the sediment. Depth did not affect Cibicides distributions except at Bay of Sails. Cibicides parasite load (the number of complete boreholes in Adamussium valves) varied by locality between 2% and 50%. For most localities the parasite load was < 20%, contrary to a previous report that ~50% of Cibicides were parasitic. The highest and lowest parasite load occurred at annual sea ice localities, suggesting that sea ice condition is not important. Rather, the number of adults that are parasitic could account for these differences. Cibicides bioerosion traces were categorized into four onto-genetic stages, ranging from newly attached recruits to parasitic adults. These traces provide an excellent proxy for population structure, revealing that Explorers Cove had a younger population than Bay of Sails. Both species are important producers of CaCO 3. Cibicides CaCO 3 biomass averaged 47-73 kg ha-1 and Adamussium averaged 4987-6806 kg ha-1 by locality. Annual production rates were much higher. Moreover, Cibicides represents 1.0-2.3% of the total host-parasite CaCO 3 biomass. Despite living in the coldest waters on Earth, these species can contribute a substantial amount of CaCO 3 to the Ross Sea and need to be incorporated into food webs, ecosystem models, and carbonate budgets for Antarctica. Funding: NSF grants from Polar Programs Earth Sciences: ANT 0739512 and ANT 0739583. NSF grants from Office of Polar Programs (Biology): PLR 0944646 and PLR 0433575. Competing Interests: The authors have declared that no competing interests exist.
Proceedings, Death Valley Natural History Conference, 2013, 2016
The Cambrian has long been regarded as a time of dynamic morphological innovation and ecological ... more The Cambrian has long been regarded as a time of dynamic morphological innovation and ecological expansion for a wide range of epibenthic and pelagic metazoan clades. Less well documented, however, is the extent to which infaunal organisms participated in this 'Cambrian Explosion' and particularly the extent to which the infaunal lifestyle, infaunal ecosystems and complex animal-sediment interactions had developed by this time. The Death Valley region of the western United States contains one of the most complete, best-preserved and best-exposed Cambrian successions in the world, providing the ideal natural laboratory to pursue questions concerning the evolutionary and environmental context in which early metazoan seafloor ecosystems first became established and the nature and pace of Cambrian infaunalization. Herein we present sedimentological, ichnological and paleoecological data from the lower Cambrian succession (Wood Canyon Formation, Zabriskie Quartzite and Carrara Formation) of Death Valley, as exposed in Echo Canyon, Death Valley National Park. We find evidence for well-developed infaunalization, consisting of dense and diverse trace fossil assemblages, characterized be significant paleobiological and paleoecological complexity, even as early as the latest early Cambrian and across a wide range of shallow marine environments. We also find that evidence of advanced infaunalization occurs in conjunction with poorly developed ichnofabrics, suggesting that, although a wide range of organisms had colonized the seafloor and engaged in various complex infaunal behaviors by the early Cambrian, the development of true infaunal mixing or bioturbation lagged behind other advances in infaunal ethology.
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Papers by Dr. Leanne G Hancock
employed redox indicators, including iron (Fe) speciation and redox-sensitive trace metal concentrations (Mo, U, V), to constrain paleoredox conditions from three Monterey locations: the Santa Barbara Basin, the Santa Maria Basin, and the San Joaquin Basin. The Fe speciation
geochemistry of the Santa Barbara and Santa Maria basin sediments are consistent with a wide range of redox conditions from suboxic to euxinic. These results, in combination with associated phosphorites and trace metal enrichment patterns, indicate oscillatory redox conditions, perhaps with a chemocline that fluctuated above the sediment-water interface on seasonal or multi-year timescales. Overall, these sections were deposited in environments similar to modern phosphorite-forming and upwelling-dominated oxygen minimum zone settings such as the Peru Margin. Geochemical evidence indicates that the San Joaquin Basin was generally more restricted and more stably anoxic compared to the other two basins, perhaps more analogous to the modern Cariaco Basin, at least for the studied interval. Iron speciation in the San Joaquin
Basin reveals anoxia and euxinia over the entirety of the studied interval, although trace metal concentrations are generally at the low end of those typical of anoxic/euxinic conditions—consistent with a restricted connection with the open ocean. The one exception is an interval c.
~11.6 million years ago (Ma) with elevated concentrations of redox-sensitive elements that may represent a decrease in basin restriction or an increase in water column sulfide concentrations. The present-day California Margin does not achieve euxinic conditions in similar basinal settings comparable with those of our Monterey sections, suggesting fundamental differences for the Miocene California margin that may carry implications for global-scale oxygen deficiency in Miocene oxygen minimum zones.
employed redox indicators, including iron (Fe) speciation and redox-sensitive trace metal concentrations (Mo, U, V), to constrain paleoredox conditions from three Monterey locations: the Santa Barbara Basin, the Santa Maria Basin, and the San Joaquin Basin. The Fe speciation
geochemistry of the Santa Barbara and Santa Maria basin sediments are consistent with a wide range of redox conditions from suboxic to euxinic. These results, in combination with associated phosphorites and trace metal enrichment patterns, indicate oscillatory redox conditions, perhaps with a chemocline that fluctuated above the sediment-water interface on seasonal or multi-year timescales. Overall, these sections were deposited in environments similar to modern phosphorite-forming and upwelling-dominated oxygen minimum zone settings such as the Peru Margin. Geochemical evidence indicates that the San Joaquin Basin was generally more restricted and more stably anoxic compared to the other two basins, perhaps more analogous to the modern Cariaco Basin, at least for the studied interval. Iron speciation in the San Joaquin
Basin reveals anoxia and euxinia over the entirety of the studied interval, although trace metal concentrations are generally at the low end of those typical of anoxic/euxinic conditions—consistent with a restricted connection with the open ocean. The one exception is an interval c.
~11.6 million years ago (Ma) with elevated concentrations of redox-sensitive elements that may represent a decrease in basin restriction or an increase in water column sulfide concentrations. The present-day California Margin does not achieve euxinic conditions in similar basinal settings comparable with those of our Monterey sections, suggesting fundamental differences for the Miocene California margin that may carry implications for global-scale oxygen deficiency in Miocene oxygen minimum zones.