Chelsea A. Korpanty

Framework-forming cold-water corals (CWC) are ecosystem engineers, building and supporting deep-sea biodiversity hotspots worldwide. While spatial patterns and drivers of species distributions have been evaluated on modern CWC reefs, little is known how reef biodiversity is affected by habitat variability over geologic time - the scale at which CWC reefs initiate, thrive, and decline. Using three CWC reef sediment cores as species diversity archives, we investigated temporal trends of molluscan diversity over the last nearly equal 13 kyr from a CWC mound in the Alboran Sea to evaluate (a) how spatial patterns of CWC-associated diversity are recorded in reef sediments, (b) the potential of CWC reefs as biodiversity hotspots when coral growth is flourishing and when it is not, and (c) which palaeoceanographic conditions or habitat characteristics may be driving biodiversity. Our results reveal that at the ecosystem scale differences in molluscan assemblages are more pronounced between CWC habitats than between intervals of CWC framework (flourishing growth) and non-framework (negligible CWC growth). However, within habitats, significant differences emerge between these assemblages: lower molluscan diversity is associated with flourishing CWC growth. Significant negative correlations between molluscan diversity and palaeoceanographic conditions conducive for CWC growth (high food availability, strong hydrodynamics, optimal bottom-water temperatures and salinities, high aggradation rates indicative of flourishing CWC growth) also imply that CWC growth and relevant environmental conditions contribute to reduced molluscan diversity. Altogether, these patterns detected over geologic time resemble those observed spatially across living CWC reefs today - where competition with resources, particularly food, prevents high reef biodiversity near dense living CWC colonies. Our study demonstrates that (1) ecological paradigms of living CWC are preserved in their sedimentary record, (2) flourishing CWC growth and conditions promoting CWC growth drive habitat-scale diversity patterns, and (3) a geological approach can be applied to study long-term diversity dynamics in CWC ecosystems.

The formation of cold-water coral (CWC) mounds is commonly seen as being the result of the sustained growth of framework-forming CWCs and the concurrent supply and deposition of terrigenous sediments under energetic hydrodynamic conditions. Yet only a limited number of studies investigated the complex interplay of the various hydrodynamic, sedimentological and biological processes involved in mound formation, which, however, focused on the environmental conditions promoting coral growth. Therefore, we are still lacking an in-depth understanding of the processes allowing the on-mound deposition of hemipelagic sediments, which contribute to two thirds of coral mound deposits. To investigate these processes over geological time and to evaluate their contribution to coral mound formation, we reconstructed changes in sediment transport and deposition by comparing sedimentological parameters (grain-size distribution, sediment composition, accumulation rates) of two sediment cores collected from a Mediterranean coral mound and the adjacent seafloor (off-mound). Our results showed that under a turbulent hydrodynamic regime promoting coral growth during the Early Holocene, the deposition of fine siliciclastic sediments shifted from the open seafloor to the coral mounds. This led to a high average mound aggradation rate of >130 cm kyr(-1), while sedimentation rates in the adjacent off-mound area at the same time did not exceed 10 cm kyr(-1). Thereby, the baffling of suspended sediments by the coral framework and their deposition within the ecological accommodation space provided by the corals seem to be key processes for mound formation. Although, it is commonly accepted that these processes play important roles in various sedimentary environments, our study provided for the first time, core-based empirical data proving the efficiency of these processes in coral mound environment. In addition, our approach to compare the grain-size distribution of the siliciclastic sediments deposited concurrently on a coral mound and on the adjacent seafloor allowed us to investigate the integrated influence of coral mound morphology and coral framework on the mound formation process. Based on these results, this study provides the first conceptual model for coral mound formation by applying sequence stratigraphic concepts, which highlights the interplay of the coral-framework baffling capacity, coral-derived ecological accommodation space and sediment supply.

The mass die‐off of Caribbean corals has transformed many of this region’s reefs to macroalgal‐dominated habitats since systematic monitoring began in the 1970s. Although attributed to a combination of local and global human stressors, the lack of long‐term data on Caribbean reef coral communities has prevented a clear understanding of the causes and consequences of coral declines. We integrated paleoecological, historical, and modern survey data to track the occurrence of major coral species and life‐history groups throughout the Caribbean from the prehuman period to the present. The regional loss of Acropora corals beginning by the 1960s from local human disturbances resulted in increases in the occurrence of formerly subdominant stress‐tolerant and weedy scleractinian corals and the competitive hydrozoan Millepora beginning in the 1970s and 1980s. These transformations have resulted in the homogenization of coral communities within individual countries. However, increases in stress‐tolerant and weedy corals have slowed or reversed since the 1980s and 1990s in tandem with intensified coral bleaching and disease. These patterns reveal the long history of increasingly stressful environmental conditions on Caribbean reefs that began with widespread local human disturbances and have recently culminated in the combined effects of local and global change.
We integrated paleoecological, historical, and modern survey data to track the prevalence of major coral species and life‐history groups throughout the Caribbean from the prehuman period to present. This extended time series reveals that Caribbean coral communities have been transformed via three distinct stages since humans: (a) declines in competitive corals by the 1960s, (b) increases in stress‐tolerant and weedy corals occurring by the 1970s and 1980s, and (c) declines or leveling‐off of stress‐tolerant and weedy corals since the 1980s or 1990s. These patterns reveal the long history of increasingly stressful environmental conditions on Caribbean reefs that began with widespread local human disturbances and have recently culminated in the combined effects of local and global change.

International Ocean Discovery Program (IODP) Expedition 356 Site U1461 represents one of the few records from the North West Australian shelf that provides information about aridity fluctuations in Australia during the Quaternary. A combination of chronostratigraphic indicators revealed the (partial) preservation of two major glaciations (Marine Isotope Stage (MIS) 2 and MIS 12) in the sedimentary record. The faunal content (mainly benthic foraminifera, corals and bryozoans) was analyzed to estimate paleo-environments and paleo-depths in order to determine if these sediments have been remobilized by reworking processes. Despite the occurrence of a depositional hiatus (including MIS 5d to MIS 9-time interval), the excellent preservation of faunal content suggests that the preserved sediment is in situ. The geochemical composition of the sediments (Nd and major elements) indicates that during MIS 12 riverine input was likely reduced because of enhanced aridity, and the sediment provenance (mainly atmospheric dust) is likely in the central (Lake Eyre) or eastern (Murray Darling Basin) parts of the Australian continent. MIS 2 is confirmed to be one of the driest periods recorded in Australia but with mixed dust sources from the eastern and western parts of the continent. More humid conditions followed the glacial maximum, which might correspond to the peak of the Indian-Australian Summer Monsoon.

The mass mortality of acroporid corals has transformed Caribbean reefs from coral- to macroalgal-dominated habitats since systematic monitoring began in the 1970s. Declines have been attributed to overfishing, pollution, sea urchin and coral disease, and climate change, but the mechanisms are unresolved due to the dearth of pre-1970s data. We used paleoecological, historical, and survey data to track
presence and dominance throughout the Caribbean from the prehuman period to present. Declines in dominance from prehuman values first occurred in the 1950s for
and the 1960s for
, decades before outbreaks of acroporid disease or bleaching. We compared trends in
dominance since 1950 to potential regional and local drivers. Human population negatively affected and consumption of fertilizer for agriculture positively affected
dominance, the latter likely due to lower human presence in agricultural areas. The earlier, local roots of Caribbean
declines highlight the urgency of mitigating local human impacts.

Cold-water corals (CWC) contribute to biodiversity and serve as ecosystem engineers on continental margins worldwide. CWC mounds - built over geologic time by the interplay of biological, sedimentological, and oceanographic processes - provide habitats for a variety of macrobenthic taxa (e.g. molluscs, sponges, bryozoans). When compared with off-mound palaeoceanographic records, coral mound records offer ecological insights about the temporal and spatial drivers and dynamics of these deep-sea ecosystems. While surficial distribution patterns of living and recently-dead mound macrobenthic communities have been described, their temporal ecological relationship with mound formation is largely unexplored. Therefore, focusing on a single taxonomic group with high preservation potential, this study aims to 1) assess quantitatively temporal ecological trends of coral mound molluscan assemblages (bivalves and gastropods), and 2) correlate those data with coral growth and palaeoceanographic records. Our goal is to determine if and how a fossil molluscan assemblage time series can act as a proxy to the biological, sedimentological, and oceanographic factors influencing CWC mound development. Preliminary results from a coral mound gravity core through Brittlestar Ridge I in the Alboran Sea, western Mediterranean ( approximately 13.2 - 2.9 ka) indicate that throughout the core bivalves are more abundant and diverse than gastropods. However, these taxonomic groups yield generally similar downcore trends in abundance and diversity. Peak molluscan assemblages (defined by high abundance and or diversity) are significantly similar in composition and primarily alternate, rather than coincide, with periods of pronounced coral growth, which are associated with high productivity during the Bolling-Allerod interstadial (13.5-12.8 ka) and Early Holocene (11.3-9.8 ka). Further ecological and statistical assessments, including a comparative study with an adjacent coral mound gravity core, will refine our understanding of the ecological relevance of molluscan assemblages to the development, demise, and cyclicity of CWC mound ecosystems.

Marine ooids are iconic indicators of shallow seawater carbonate saturation state, and their formation has traditionally been ascribed to physicochemical processes. The Indo-Pacific stands out as a region devoid of oolites, particularly during the Quaternary: the "ooid enigma". Here we present results from recent coring by the International Ocean Discovery Program (IODP Expedition 356) off west Australia that shows that ooid horizons are common in Pleistocene strata up to 730,000 years old. Extensive "ooid factories" were created due to the presence of long-lived tidally influenced flat-topped tropical platforms suitable for intermittent ooid accretion over hundreds to thousands of years during highstands and times of lower sea level. This work suggests marine ooids may actually be more common in Indo-Pacific than previously reported. Past global ocean alkalinity was elevated during Pleistocene glacial periods and continental climate was generally more arid in the Indo-Pacific region compared to interglacials and the Holocene. Therefore, increased aridity associated with higher alkalinity conditions during the glacials facilitated ooid precipitation on adjacent tropical carbonate platforms particularly offshore from arid Australia. This confluence of factors suggests that more "ooid factories" may be encountered by further coring Indo-Pacific regions with Pleistocene flat long-lived carbonate shelves. However, Indo-Pacific Quaternary ooid occurrences outside Australia are rare, suggesting that the Northwest Shelf may be a unique archive of this non-skeletal precipitate. Further investigations into the petrography and geochemistry of pre-Holocene ooid occurrences will provide insights into their origin and the relative role of biotic, physicochemical and other factors in their formation.

The Indonesian Throughflow (ITF) transports warm water from the Indo-Pacific Warm Pool to the Indian Ocean, influences the thermohaline conveyor circulation and global climate, and drives the Leeuwin Current - a warm, low-salinity, nutrient-deficient, southerly-flowing current along Australia's Northwest Shelf (NWS). Prior studies suggest strength and extent of the Leeuwin Current varied over the Quaternary, but increased approximately 1 Ma, facilitating expansion of tropical marine biota along Western Australia. To obtain a detailed history of the ITF and Leeuwin Current, International Ocean Discovery Program (IODP) Expedition 356 drilled sediments at 7 NWS sites spanning 29 degrees -18 degrees S. In situ solitary azooxanthellate scleractinian corals from these cores will be combined with other biostratigraphic and sedimentologic evidence (e.g. D (super 18) O, D (super 13) C, U, K, Th, sediment grain size, foraminiferal abundances) to reconstruct paleoenvironments on the NWS. A total of 183 fossil corals, with estimated ages of <1.6 - 0.29 Ma, have been recovered. They are now being identified, their temporal and spatial distributions determined, and ecological settings inferred from literature and (paleo)ecological databases. Selected corals will be isotopically dated to refine age models. The 100 specimens identified to lowest possible taxonomic level represent 21 species, 17 genera, and 5 families. They include new Western Australian records for 1 genus and 11 species, the first fossil occurrences of 1 genus and 14 species, and 1 newly described species. Of 9 species previously known from Western Australia, 7 are considered tropical taxa and 2 temperate taxa. To date, only 18 fossil azooxanthellate coral specimens (Late Cretaceous - Late Pleistocene) have been reported for Western Australia. This new collection thereby increases the number of fossil specimens in the region by 10 times. In addition to providing new insights to the history of the ITF and Leeuwin Current, this collection expands understanding of the global and temporal diversity of solitary corals and highlights the challenges and necessity of studying deep-water organisms and ecosystems.