Ecological extinction caused by overfishing precedes all other pervasive human disturbance to coastal ecosystems, including pollution, degradation of water quality, and anthropogenic climate change. Historical abundances of large consumer species were fantastically large in comparison with recent observations. Paleoecological, archaeological, and historical data show that time lags of decades to centuries occurred between the onset of overfishing and consequent changes in ecological communities, because unfished species of similar trophic level assumed the ecological roles of overfished species until they too were overfished or died of epidemic diseases related to overcrowding. Retrospective data not only help to clarify underlying causes and rates of ecological change, but they also demonstrate achievable goals for restoration and management of coastal ecosystems that could not even be contemplated based on the limited perspective of recent observations alone.

/pdf/historical-overfishing-and-the-recent-collapse-of-coastal-28k1p5mqjm.pdf

Historical overfishing and the recent collapse of coastal ecosystems.

https://homepages.uc.edu/~algeot/Tribovillard-Algeo-etal-CG-2006.pdf

Trace metals as paleoredox and paleoproductivity proxies: An update

Sedimentary organic matter preservation: an assessment and speculative synthesis

The second edition of The Biomarker Guide is a fully updated and expanded version of this essential reference. Now in two volumes, it provides a comprehensive account of the role that biomarker technology plays both in petroleum exploration and in understanding Earth history and processes. Biomarkers and Isotopes in the Environment and Human History details the origins of biomarkers and introduces basic chemical principles relevant to their study. It discusses analytical techniques, and applications of biomarkers to environmental and archaeological problems. The Biomarker Guide is an invaluable resource for geologists, petroleum geochemists, biogeochemists, environmental scientists and archaeologists.

The Biomarker Guide

Comparison of geochemical indices used for the interpretation of palaeoredox conditions in ancient mudstones

Abstract The characteristics of mid-latitude shelf seas are primarily controlled by seasonal cyclicity in wind-driven mixing. Seasonal dysoxic-anoxic conditions may occur in summer in salinity-stratified estuarine or pro-delta settings, or more extensively in those open shelf areas where a total depth of ≤60 m and the seasonal thermocline result in a bottom water layer ≤10 m thick. When bottom circulation is limited the oxygen stored in this layer may become periodically exhausted if climatic factors extend the stratified period to seven or more months, or if there is additional organic loading (via flagellate blooms and/or pollution). This causes widespread mortalities and a shift to soft-bodied, non-fossilizing benthic faunas. Our review supports seasonal dysoxia-anoxia as being the best model to account for the key characteristics of many ancient epeiric sea black shales. It would appear that the latter rarely represent true continuous anoxia except locally in more-confined deeper sub-basins. We recommend that the following terms should be applied to environments, facies, or oxygenation levels: oxic (8.0–2.0 ml/l O2), dysoxic (2.0–0.2 ml/l), suboxic (0.2–0.0 ml/l) and anoxic (0.0 ml/l). The corresponding biofacies terms are: aerobic, dysaerobic, quasianaerobic (laminated, without macrofauna, but with in situ benthic microfauna) and anaerobic. Hypoxic and normoxic should only be used with regard to the physiological responses of living organisms.

Modern and ancient continental shelf anoxia: an overview

Drs. R. V. Tyson and T. H. Pearson convened a symposium on modern and ancient shelf anoxia in May, 1989 under the aegis of the Gologica] Society Marine Studies Group. This volume is the product of that meeting. The meeting was multidisciplinary including geologists, biologists and chemists. The examination and interpretation of anoxic sedimentary environments is of significance in our understanding of the interplay of organic production, water circulation and sediment accumulation. When the flux of degradable organic material exceeds the oxygen supply, then anoxia and the exclusion of macrobenthos removes the more common bioturbation effects preserving primary depositional structures. It has also been postulated that the anoxic environment permits preservation of a larger proportion of the incoming organic matter. Studies in a variety of modern environments has tended to argue against that hypothesis although certainly the role of sulfate reducing bacteria versus aerobic bacterial processes is a major factor in the ultimate sedimentary product. Within the broad spectrum of anoxic environments, shelf anoxia is a special case. One complicating factor for the stratigrapher is that the anoxic condition in several shelf environments discussed in these papers is temporary and ephemeral. Thus a primary question is what artifacts of these periods of low or zero oxygen will remain in the sedimentary record? As the convenors point out in their opening review, the modern effects impact fisheries and with the overprinting of anthropogenic effects produce some complex questions for the marine biologist. They also aver that much of the hydrocarbon-rich sedimentary resources were laid down and developed in organic-rich and oxygen-depleted depositional environments. As noted earlier, the sometimes higher organic content of such sediments reflects the common association of high productivity regions (upwelling regions) with oxygen-deficient depositional environments. Even if degradation and removal rates are similar for all depositional environments, certainly the net input under high production areas will be larger. Major factors influencing oxygendeficiency in shelf regions are the higher biological production in margins as compared to open ocean, the short fall path in margins compared to open oceans and resulting higher sediment input rates, higher sediment accumulation rates and thus thicker mass accumulation and higher burial rates for carbon. Bioturbation is also operating at higher rates, and fluctuations in depositional regime are larger and faster. The editors also introduce a suggested standard terminology for such environments in which the environmental facies are termed oxic, dysoxic (with subdivisions), suboxic and anoxic with respective bottom water oxygen contents of > 2.0 ml/L, 0.2-2.0 ml/L, 0-0.2 ml/L and <0.0 ml/L (increasing dissolved H2S). Biofacies terms for these are respectively aerobic, dysaerobic, quasi-anaerobic and anaerobic at the same oxygen boundaries. Physiological regimes would be Normoxic, Hypoxic (no matching term for Suboxic) and anoxic respectively. The volume is subdivided into modern shelf anoxia studies, and ancient shelf anoxia studies. The papers in the two sections number 11 and 16 respectively and space does not permit review of each paper. The modern studies examine the northern Gulf Of Mexico shelf associated with or adjacent to the Mississippi River discharge (papers by Boesch and Rabalais; Rabalais, Turner, Wiseman and Boesch; Harper, McKinney, Nance and Salzer)) which discuss effects on benthos, recovery of communities and general oceanographic characteristics of the environment. This area may well be one in which the anoxia has an anthropogenic source as noted in the paper by Rabalais and others. Contrasts with other areas are noted. The effects are of the order of 4-5 months in duration in the delta front area. A paper by Van der Zwaan and Jorissen compares the effects in the northern Adriatic, Orinoco-Paria shelf and the Mississippi locale. All are influenced by high river discharges and pollution effects. The authors utilize benthic foraminifera as indi-

Modern and Ancient Continental Shelf Anoxia

Total organic carbon, organic phosphorus, and biogenic barium fluxes as proxies for paleomarine productivity

Sedimentation rate, dilution, preservation and total organic carbon: some results of a modelling study

Summary This paper attempts to demonstrate that the multi-disciplinary philosophy behind palynofacies investigations is of great value to the meaningful interpretation of the origins and palaeoenvironment of marine petroleum source rocks (MPSRs). The key control on the formation of MPSRs is identified as bottom water oxygenation (correlated with the location of the Eh interface and the intensity of macrobenthic activity). Particular emphasis is placed on the necessity for greater accuracy in the terminology used to describe levels of oxygenation. Aerobic environments are characterized by organically lean sediments (0–3.0% TOC) with Type III kerogen assemblages composed of relatively refractory land plant debris or highly degraded, marine-derived, amorphous organic matter (AOM). Their organic richness is largely dependent on sediment accumulation rate and proximity to sources of terrestrial organic matter supply. They produce mainly gas at maturation. Dysaerobic to anoxic environments are characterized by MPSR facies with high TOC values and Type II kerogen assemblages dominated by relatively lipid-rich AOM. These represent the classic ‘black shale’ source rocks and are the main source of petroleum in marine basins. Except where they are redeposited, dinocysts are characteristically absent or rare in marine ‘black shales’. They are mainly produced in unstable, seasonally mixed water masses and may consequently be regarded as indices of hydrographic stability. Prasinophycean phycomas, which differ from dinocysts in their function, are often the dominant, or most conspicuous, marine palynomorphs of pelagic sediments and stably stratified ‘black shale’ basins.

R. V. Tyson

Papers

Modern and ancient continental shelf anoxia: an overview

Modern and Ancient Continental Shelf Anoxia

Total organic carbon, organic phosphorus, and biogenic barium fluxes as proxies for paleomarine productivity

Sedimentation rate, dilution, preservation and total organic carbon: some results of a modelling study

The genesis and palynofacies characteristics of marine petroleum source rocks