Late glacial to deglacial variation of coralgal assemblages in the Great Barrier Reef, Australia

Integrated Ocean Drilling Program (IODP) Expedition 325 cored submerged reefs along the shelf edge of the Great Barrier Reef (GBR) to study sea-level and environmental changes and their impacts on reef communities and reef growth since the Last Glacial Maximum (LGM). Previous work defined five reef sequences (Reef 1–5) that span the last 30,000 years. Here we examined the variation in coralgal assemblages and their paleoenvironmental settings in late glacial to deglacial sequences from 23 holes cored seaward of the modern GBR in water depths from 46 to 131 m along four transects at three localities: Hydrographers Passage (HYD-01C and HYD-02A), Noggin Pass (NOG–01B), and Ribbon Reef (RIB-02A). We identified three coralline algal assemblages and eight coral assemblages indicating a broad range of reef settings from the shallow reef crest (0–5 m) to the deep forereef slope (>20 m). We document in detail for the first time the distribution and composition of reef communities that grew in the GBR during the LGM from 22,000–19,000 years ago. They included coral taxa that are major reef builders today: Isopora, Acropora gr. humilis, Dipsastraea gr. pallida, Porites, and Montipora. Prior to the fall in sea level to the maximum extent of the LGM, late glacial reef communities developed more proximally (landward) to the modern GBR along the shelf edge. Their distribution and composition reflect influences of the older Pleistocene basement depth and possible terrigenous sediment inputs. Post-LGM deglacial reef growth was vigorous in proximal sites and characterized by the accretion of a very shallow high-energy coralgal assemblage composed of medium to robustly branching Acropora, including A. gr. humilis, and thick algal crusts of Porolithon gr. onkodes associated with vermetid gastropods. More distally, reef growth was variably impacted by terrigenous input following deglacial reflooding of antecedent reef terraces. The coralgal succession and sedimentary facies in Noggin Pass indicate that an early drowning trend was linked to increased turbidity that was likely controlled by shelf morphology (narrow shelf, steep slope) and/or proximity to a paleo-river mouth. The deglacial succession in Ribbon Reef lacks typical shallow-water indicators, which may reflect influences of the particularly steep slope of the northern GBR shelf edge on reef zonation. A major sea-level jump at the onset of the Younger Dryas displaced reef habitats further upslope, forming a barrier reef system mainly composed of robustly branching acroporids distinct from the more distal sites. Our results highlight the importance of sedimentation and shelf morphology in addition to relative sea-level changes in controlling variations in reef community over centennial to millennial timescales. © 2019 Elsevier B.V.Australian Research Council-DP109400

Coral record of Younger Dryas Chronozone warmth on the Great Barrier Reef

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology 35(12), (2020): e2020PA003962, doi:10.1029/2020PA003962.The Great Barrier Reef (GBR) is an internationally recognized and widely studied ecosystem, yet little is known about its sea surface temperature (SST) evolution since the Last Glacial Maximum (LGM) (~20 kyr BP). Here, we present the first paleo‐application of Isopora coral‐derived SST calibrations to a suite of 25 previously published fossil Isopora from the central GBR spanning ~25–11 kyr BP. The resultant multicoral Sr/Ca‐ and δ18O‐derived SST anomaly (SSTA) histories are placed within the context of published relative sea level, reef sequence, and coralgal reef assemblage evolution. Our new calculations indicate SSTs were cooler on average by ~5–5.5°C at Noggin Pass (~17°S) and ~7–8°C at Hydrographer's Passage (~20°S) (Sr/Ca‐derived) during the LGM, in line with previous estimates (Felis et al., 2014, https://doi.org/10.1038/ncomms5102). We focus on contextualizing the Younger Dryas Chronozone (YDC, ~12.9–11.7 kyr BP), whose Southern Hemisphere expression, in particular in Australia, is elusive and poorly constrained. Our record does not indicate cooling during the YDC with near‐modern temperatures reached during this interval on the GBR, supporting an asymmetric hemispheric presentation of this climate event. Building on a previous study (Felis et al., 2014, https://doi.org10.1038/ncomms5102), these fossil Isopora SSTA data from the GBR provide new insights into the deglacial reef response, with near‐modern warming during the YDC, since the LGM.This work was funded by National Science Foundation (NSF) award OCE 13‐56948 to B. K. L, with NSF GRFP support DGE‐11‐44155 to L. D. B., and the Australian Research Council (grant no. DP1094001) and ANZIC IODP. Partial support for B. K. L's work on this project also came from the Vetlesen Foundation via a gift to the Lamont‐Doherty Earth Observatory. T. F. received funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Project number 180346848, through Priority Program 527 “IODP.” A. T. received support from the UK Natural Environment Research Council (NE/H014136/1 and NE/H014268/1). M. T. thanks Ministry of Earth Sciences for support (NCPOR contribution no. J‐84/2020‐21). L. D. B. would also like to thank Kassandra Costa for her input regarding error analysis.2021-06-1

Response of the Great Barrier Reef to sea level and environmental changes over the past 30,000 years

Previous drilling through submerged fossil coral reefs has greatly improved our understanding of the general pattern of sea-level change since the Last Glacial Maximum, however, how reefs responded to these changes remains uncertain. Here we document the evolution of the Great Barrier Reef (GBR), the world\u27s largest reef system, to major, abrupt environmental changes over the past 30 thousand years based on comprehensive sedimentological, biological and geochronological records from fossil reef cores. We show that reefs migrated seaward as sea level fell to its lowest level during the most recent glaciation (~20.5-20.7 thousand years ago (ka)), then landward as the shelf flooded and ocean temperatures increased during the subsequent deglacial period (~20-10 ka). Growth was interrupted by five reef-death events caused by subaerial exposure or sea-level rise outpacing reef growth. Around 10 ka, the reef drowned as the sea level continued to rise, flooding more of the shelf and causing a higher sediment flux. The GBR\u27s capacity for rapid lateral migration at rates of 0.2-1.5 m yr−1 (and the ability to recruit locally) suggest that, as an ecosystem, the GBR has been more resilient to past sea-level and temperature fluctuations than previously thought, but it has been highly sensitive to increased sediment input over centennial-millennial timescales

Wiskott-Aldrich syndrome protein deficiency in innate immune cells leads to mucosal immune dysregulation and colitis in mice

BACKGROUND & AIMS: Immunodeficiency and autoimmune sequelae, including colitis, develop in patients and mice deficient in Wiskott-Aldrich Syndrome protein (WASP), a hematopoietic-specific intracellular signaling molecule that regulates the actin cytoskeleton. Development of colitis in WASP-deficient mice requires lymphocytes; transfer of T cells is sufficient to induce colitis in immunodeficient mice. We investigated the interactions between innate and adaptive immune cells in mucosal regulation during development of T-cell-mediated colitis in mice with WASP-deficient cells of the innate immune system. METHODS: Naïve and/or regulatory CD4(+) T cells were transferred from 129 SvEv mice into RAG-2 deficient (RAG-2 KO) mice or mice lacking WASP and RAG-2 (WRDKO). Animals were observed for the development of colitis; effector and regulatory functions of innate immune and T cells were analyzed with in vivo and in vitro assays. RESULTS: Transfer of unfractionated CD4(+) T cells induced severe colitis in WRDKO, but not RAG-2 KO, mice. Naïve wild-type T cells had higher levels of effector activity and regulatory T cells had reduced suppressive function when transferred into WRDKO mice compared to RAG-2 KO mice. Regulatory T-cell proliferation, generation, and maintenance of FoxP3 expression were reduced in WRDKO recipients, and associated with reduced numbers of CD103(+) tolerogenic dendritic cells and levels of interleukin (IL)-10. Administration of IL-10 prevented induction of colitis following transfer of T cells into WRDKO mice. CONCLUSIONS: Defective interactions between WASP-deficient innate immune cells and normal T cells disrupt mucosal regulation, potentially by altering the functions of tolerogenic dendritic cells, production of IL-10, and homeostasis of regulatory T cells

WASp-deficient B cells play a critical, cell-intrinsic role in triggering autoimmunity

In a manner dependent on CD4 T cell help and Toll-like receptor signals, B cells lacking WASp induce autoantibody production and autoimmune disease in mice

Rapid glaciation and a two-step sea-level plunge into The Last Glacial Maximum

The approximately 10,000-year-long Last Glacial Maximum, before the termination of the last ice age, was the coldest period in Earth’s recent climate history1. Relative to the Holocene epoch, atmospheric carbon dioxide was about 100 parts per million lower and tropical sea surface temperatures were about 3 to 5 degrees Celsius lower2,3. The Last Glacial Maximum began when global mean sea level (GMSL) abruptly dropped by about 40 metres around 31,000 years ago4 and was followed by about 10,000 years of rapid deglaciation into the Holocene1. The masses of the melting polar ice sheets and the change in ocean volume, and hence in GMSL, are primary constraints for climate models constructed to describe the transition between the Last Glacial Maximum and the Holocene, and future changes; but the rate, timing and magnitude of this transition remain uncertain. Here we show that sea level at the shelf edge of the Great Barrier Reef dropped by around 20 metres between 21,900 and 20,500 years ago, to −118 metres relative to the modern level. Our findings are based on recovered and radiometrically dated fossil corals and coralline algae assemblages, and represent relative sea level at the Great Barrier Reef, rather than GMSL. Subsequently, relative sea level rose at a rate of about 3.5 millimetres per year for around 4,000 years. The rise is consistent with the warming previously observed at 19,000 years ago1,5, but we now show that it occurred just after the 20-metre drop in relative sea level and the related increase in global ice volumes. The detailed structure of our record is robust because the Great Barrier Reef is remote from former ice sheets and tectonic activity. Relative sea level can be influenced by Earth’s response to regional changes in ice and water loadings and may differ greatly from GMSL. Consequently, we used glacio-isostatic models to derive GMSL, and find that the Last Glacial Maximum culminated 20,500 years ago in a GMSL low of about −125 to −130 metres.Financial support of this research was provided by the JSPS KAKENHI (grant numbers JP26247085, JP15KK0151, JP16H06309 and JP17H01168), the Australian Research Council (grant number DP1094001), ANZIC, NERC grant NE/H014136/1 and Institut Polytechnique de Bordeaux