Lohmann George P.

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Lohmann
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George P.
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  • Technical Report
    PATS-1 : a package of programs for the analysis of marine micropaleontological data on the Vax 11/780 computer
    (Woods Hole Oceanographic Institution, 1980-06) Lohmann, George P.
    PATS-l is the first version of a package of computer programs and subroutines written or acquired specifically for the archiving, analysis, and presentation of marine micropaleontological data. The aim of this report is to document the procedures and programs incorporated in PATS-l and make them available to colleagues working on closely related research problems. The program package described in this report is not intended to be either comprehensive or generally useful. Rather, the PATS-l package was assembled for a specific purpose. It reflects the solutions to problems encountered in the course of my own work in micropaleontological oceanography. Some programs are so strictly tailored to my own research that they may have to be modified to be of any use to others. However, where convenient I have tried to generalize programs, especially in design of the subroutines incorporated into the PATS-l/LIBRARY. This report provides program listings, documentation, examples and instructions for implementation and use of the PATS-l package. Programs were written to be used interactively and at WHOI are run exclusively on the time-sharing system of the VAX ll/780 computer.
  • Technical Report
    Oceanographic significance of Pacific late Miocene clacareous nannoplankton
    (Woods Hole Oceanographic Institution, 1980-12) Lohmann, George P. ; Carlson, Jodell J.
    An analysis of the variability in the composition and distribution of Pgcific Late Miocene calcareous nannoplankton about their average biogeography shows that there are primarily two environmental factors causing that variability, climate and dissolution. Climate produces a latitudinal, biogeographic differentiation of the Late Miocene nannoflora, while selective dissolution superimposes a bathymetric differentiation of the nannoflora on that due to climate. Together, these two factors produce three distinct Late Miocene nannofloral assemblages, a high-latitude, temperate assemblage characterized by Reticulofenestra pseudoumbilica and Coccolithus pelagicus, and two tropical assemblages, their differences in composition depending on water depth and surface-water productivity: (1) in shallower water and beneath areas of higher organic productivity there is an undissolved assemblage characterized by sphenoliths, small elliptical placoliths and Coccolithus pataecus; (2) in deeper water and areas of lower productivity there is a dissolved assemblage dominated by discoasters. Selective dissolution produces most of the apparent biogeographic variation in Pacific Late Miocene nannoplankton compositions, the variation in compositions observed between the 17 sites studied. Dissolution preferentially removes the more-soluble constituents of the tropical nannoflora so that increasing dissolution tends to give tropical nannoflora a cooler water aspect. At the same time, selective dissolution shifts the composition of the warmer water component towards its more resistant taxa. This produces an assemblage typical of deeper tropical waters and areas of lower productivity. Nannoplankton records show a period of greatly decreased calcite dissolution in deep tropical and temperate South Pacific sites between 8 and 10 m.y. ago. This decrease is strongly correlated with an increase in the δC-13 composition of Pacific deep waters. Calcite dissolution increased during this same period in the deep North Pacific. Nannoplankton records of Late Miocene climate in the tropics are distinctly different from those at higher, south temperate latitudes. Tropical records show a sharp warming in the earliest Late Miocene after a generally cool late Middle Miocene. This was followed by a temporary cooling, nearly to Middle Miocene levels, about 7 m.y. ago. Toward the end of the Late Miocene, the tropical Pacific warmed again and remained warm into the Pliocene . Warming of temperate climates was much more gradual. Not until latest Miocene did the southern temperate latitudes warm appreciably; they continued warming into the Pliocene. This rapid warming of the tropics and gradual warming farther south produced a temporary increase in the latitudinal climatic gradient across the southern Pacific Ocean 8 to 10 m.y. ago. On the basis of the nannoplankton oceanographic records we postulate that beginning 10 m.y. ago the production of deep and bottom waters in the Southern Ocean increased. This produced the northward decrease in calcite preservation, the increase in benthic δC-13, and the strong climatic gradient across southern latitudes. This period of increase deep Pacific circulation ended 7.5 rn.y. ago.
  • Article
    Repeat bleaching of a central Pacific coral reef over the past six decades (1960–2016)
    (Nature Publishing Group, 2018-11-08) Barkley, Hannah C. ; Cohen, Anne L. ; Mollica, Nathaniel R. ; Brainard, Russell E. ; Rivera, Hanny E. ; DeCarlo, Thomas M. ; Lohmann, George P. ; Drenkard, Elizabeth J. ; Alpert, Alice ; Young, Charles W. ; Vargas-Ángel, Bernardo ; Lino, Kevin C. ; Oliver, Thomas A. ; Pietro, Kathryn R. ; Luu, Victoria
    The oceans are warming and coral reefs are bleaching with increased frequency and severity, fueling concerns for their survival through this century. Yet in the central equatorial Pacific, some of the world’s most productive reefs regularly experience extreme heat associated with El Niño. Here we use skeletal signatures preserved in long-lived corals on Jarvis Island to evaluate the coral community response to multiple successive heatwaves since 1960. By tracking skeletal stress band formation through the 2015-16 El Nino, which killed 95% of Jarvis corals, we validate their utility as proxies of bleaching severity and show that 2015-16 was not the first catastrophic bleaching event on Jarvis. Since 1960, eight severe (>30% bleaching) and two moderate (<30% bleaching) events occurred, each coinciding with El Niño. While the frequency and severity of bleaching on Jarvis did not increase over this time period, 2015–16 was unprecedented in magnitude. The trajectory of recovery of this historically resilient ecosystem will provide critical insights into the potential for coral reef resilience in a warming world.
  • Article
    Mass coral mortality under local amplification of 2°C ocean warming
    (Nature Publishing Group, 2017-03-23) DeCarlo, Thomas M. ; Cohen, Anne L. ; Wong, George T. F. ; Davis, Kristen A. ; Lohmann, George P. ; Soong, Keryea
    A 2°C increase in global temperature above pre-industrial levels is considered a reasonable target for avoiding the most devastating impacts of anthropogenic climate change. In June 2015, sea surface temperature (SST) of the South China Sea (SCS) increased by 2 °C in response to the developing Pacific El Niño. On its own, this moderate, short-lived warming was unlikely to cause widespread damage to coral reefs in the region, and the coral reef “Bleaching Alert” alarm was not raised. However, on Dongsha Atoll, in the northern SCS, unusually weak winds created low-flow conditions that amplified the 2°C basin-scale anomaly. Water temperatures on the reef flat, normally indistinguishable from open-ocean SST, exceeded 6°C above normal summertime levels. Mass coral bleaching quickly ensued, killing 40% of the resident coral community in an event unprecedented in at least the past 40 years. Our findings highlight the risks of 2°C ocean warming to coral reef ecosystems when global and local processes align to drive intense heating, with devastating consequences.
  • Article
    Community production modulates coral reef pH and the sensitivity of ecosystem calcification to ocean acidification
    (John Wiley & Sons, 2017-01-31) DeCarlo, Thomas M. ; Cohen, Anne L. ; Wong, George T. F. ; Shiah, Fuh-Kwo ; Lentz, Steven J. ; Davis, Kristen A. ; Shamberger, Kathryn E. F. ; Lohmann, George P.
    Coral reefs are built of calcium carbonate (CaCO3) produced biogenically by a diversity of calcifying plants, animals, and microbes. As the ocean warms and acidifies, there is mounting concern that declining calcification rates could shift coral reef CaCO3 budgets from net accretion to net dissolution. We quantified net ecosystem calcification (NEC) and production (NEP) on Dongsha Atoll, northern South China Sea, over a 2 week period that included a transient bleaching event. Peak daytime pH on the wide, shallow reef flat during the nonbleaching period was ∼8.5, significantly elevated above that of the surrounding open ocean (∼8.0–8.1) as a consequence of daytime NEP (up to 112 mmol C m−2 h−1). Diurnal-averaged NEC was 390 ± 90 mmol CaCO3 m−2 d−1, higher than any other coral reef studied to date despite comparable calcifier cover (25%) and relatively high fleshy algal cover (19%). Coral bleaching linked to elevated temperatures significantly reduced daytime NEP by 29 mmol C m−2 h−1. pH on the reef flat declined by 0.2 units, causing a 40% reduction in NEC in the absence of pH changes in the surrounding open ocean. Our findings highlight the interactive relationship between carbonate chemistry of coral reef ecosystems and ecosystem production and calcification rates, which are in turn impacted by ocean warming. As open-ocean waters bathing coral reefs warm and acidify over the 21st century, the health and composition of reef benthic communities will play a major role in determining on-reef conditions that will in turn dictate the ecosystem response to climate change.