The Effects of an early Eocene Paleogene Hyperthermal on the Benthic Ocean

Deep-sea benthic foraminiferal turnover across early Eocene hyperthermal events at Northeast Atlantic DSDP Site 550

Authors:

Arreguín-Rodríguez et al

Abstract:

Several extreme warming events, called hyperthermals, superimposed the warming trend of the early Paleogene. Deep-sea benthic foraminifera suffered major extinction during the most severe of those events, the Paleocene–Eocene Thermal Maximum, but their response to the following, less severe hyperthermals has been documented at very few locations. We evaluate and compare the benthic foraminiferal assemblages across ETM2 and H2 events at DSDP Site 550 in the NE Atlantic Ocean. The CIE and carbonate dissolution were more severe during ETM2 than during the H2 event.

Early Eocene benthic foraminiferal assemblages were moderately diverse and strongly dominated by calcareous taxa, and they consisted of mixed infaunal and epifaunal morphogroups. They responded similarly to ETM2 and H2 events, showing a decrease in absolute abundance, an increase in the relative abundance of agglutinated taxa, indicative of more carbonate-corrosive waters, and a marked decrease in the percentage of Bolivinoides decoratus, suggesting a lower food supply during hyperthermals. However, some differences in their response were also noted. Oligotrophic taxa such as Nuttallides truempyi and Quadrimorphina profunda increased in relative abundance during early ETM2, whereas Globocassidulina subglobosa and Osangularia sp. 1, opportunistic species which may indicate pulsed food inputs, peaked during the H2 event. We conclude that both hyperthermal events represent a general disruption of an overall meso-oligotrophic environment, with less food reaching the seafloor combined with increased CaCO3 corrosivity of bottom waters. We did not find clear evidence for decreasing primary productivity during the hyperthermal events, and the apparent low food delivery to the seafloor may have been related to an increase in benthic foraminiferal metabolic rates due to the higher temperatures, with a more severe lack of food during ETM2 than during H2. The benthic foraminiferal response thus appears to be scaled to the magnitude of hyperthermals.

Recovery of the Benthic Community in the Tethys After the Permian Triassic Extinction

Environmental controls on the post-Permian recovery of benthic, tropical marine ecosystems in western Palaeotethys (Aggtelek Karst, Hungary)

Authors:

Foster et al

Abstract:

Climate warming during the late Permian is associated with the most severe mass extinction event of the Phanerozoic, and the expansion of hypoxic and anoxic conditions in shallow shelf settings. It has been hypothesised that wave aeration provided a ‘habitable zone’ in the shallowest environments that allowed the survival and rapid recovery of benthic invertebrates during the Early Triassic. We test this hypothesis by studying the rock and fossil records of the Aggtelek Karst, Hungary. Nearshore settings recorded in the Bódvaszilas Sandstone Formation and units A and D of the Szin Marl Formation are characterised by taxonomically homogenous fossil assemblages of low diversity and low evenness. Ecological and taxonomic recovery in this environmental setting was hampered by persistent environmental stress. This stress is attributed to increased runoff related to climate warming during the Early Triassic that resulted in large salinity fluctuations, increased sedimentation rates and eutrophication that led to seasonal hypoxia and an environment only favourable for opportunistic taxa. In contrast, shoal and mid-ramp settings further offshore are characterised by high diversity faunas with a greater functional complexity. Prior to the late Spathian Tirolites carniolicus Zone, the shelly fossils and trace fossils are limited to settings aerated by wave activity, which supports the habitable zone hypothesis. In the Tirolites carniolicus Zone, however, the oxygen minimum zone retreats offshore and the habitable deeper shelf settings are rapidly colonised by shallow water taxa, evidenced by the highest levels of diversity and bioturbation recorded in the study. Locally, full recovery of marine ecosystems is not recorded until the Illyrian, with the establishment of a sponge reef complex.

Fossils of a 'Lost City' Hydrothermal Ecology From Cretaceous Spain

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

Authors:

Klein et al

Abstract:

Subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle (i.e., serpentinite). However, geosphere-biosphere interactions in serpentinite-hosted subseafloor mixing zones remain poorly constrained. Here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a Cretaceous Lost City-type hydrothermal system at the magma-poor passive Iberia Margin (Ocean Drilling Program Leg 149, Hole 897D). Brucite−calcite mineral assemblages precipitated from mixed fluids ca. 65 m below the Cretaceous paleo-seafloor at temperatures of 31.7 ± 4.3 °C within steep chemical gradients between weathered, carbonate-rich serpentinite breccia and serpentinite. Mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity. Dense microbial colonies are fossilized in brucite−calcite veins that are strongly enriched in organic carbon (up to 0.5 wt.% of the total carbon) but depleted in 13C (δ13CTOC = −19.4‰). We detected a combination of bacterial diether lipid biomarkers, archaeol, and archaeal tetraethers analogous to those found in carbonate chimneys at the active Lost City hydrothermal field. The exposure of mantle rocks to seawater during the breakup of Pangaea fueled chemolithoautotrophic microbial communities at the Iberia Margin, possibly before the onset of seafloor spreading. Lost City-type serpentinization systems have been discovered at midocean ridges, in forearc settings of subduction zones, and at continental margins. It appears that, wherever they occur, they can support microbial life, even in deep subseafloor environments.

The Survivors of the Permian Mass Extinction Delayed Benthic Marine Recovery

Competition in slow motion: the unusual case of benthic marine communities in the wake of the end-Permian mass extinction

Authors:

Hautmann et al

Abstract:

Changes of community structure in response to competition usually take place on timescales that are much too short to be visible in the geological record. Here we report the notable exception of a benthic marine community in the wake of the end-Permian mass extinction, which is associated with the microbial limestone facies of the earliest Triassic of South China. The newly reported fauna is well preserved and extraordinarily rich (30 benthic macroinvertebrate species, including the new species Astartella? stefaniae (Bivalvia) and Eucochlis obliquecostata (Gastropoda)) and stems from an environmentally stable setting providing favourable conditions for benthic organisms. Whereas changes in the taxonomic composition are negligible over the observed time interval of 10–100 ka, three ecological stages are identified, in which relative abundances of initially rare species continuously increased at the cost of previously dominant species. Concomitant with the changes of dominant species is an increase in faunal evenness and heterogeneity. In the absence of both environmental and taxonomic changes, we attribute this pattern to the long-term effects of interspecific competition, which acted at an unusually slow pace because the number of competing species and potential immigrants was dramatically reduced by the end-Permian mass extinction. We suggest that these non-actualistic conditions led to decreased rates of niche differentiation and hence to the delayed rediversification of benthos that characterizes the aftermath of the greatest Phanerozoic mass extinction event. A hyperbolic diversification model is proposed, which accounts for the positive relationship between the intensity of interspecific competition and the rate of niche differentiation and resolves the conundrum of delayed rediversification at a time when niche space was largely vacated.

Implications of Quartez Embedded Biogenic Iron-Rich Filaments From Ediacaran NeoProterozoic China

Biogenic Iron-Rich Filaments in the Quartz Veins in the Uppermost Ediacaran Qigebulake Formation, Aksu Area, Northwestern Tarim Basin, China: Implications for Iron Oxidizers in Subseafloor Hydrothermal Systems

Authors:

Zhou et al

Abstract:

Fe-(oxyhydr)oxide-encrusted filamentous microstructures produced by microorganisms have been widely reported in various modern and ancient extreme environments; however, the iron-dependent microorganisms preserved in hydrothermal quartz veins have not been explored in detail because of limited materials available. In this study, abundant well-preserved filamentous microstructures were observed in the hydrothermal quartz veins of the uppermost dolostones of the terminal-Ediacaran Qigebulake Formation in the Aksu area, northwestern Tarim Basin, China. These filamentous microstructures were permineralized by goethite and hematite as revealed by Raman spectroscopy and completely entombed in chalcedony and quartz cements. Microscopically, they are characterized by biogenic filamentous morphologies (commonly 20–200 μm in length and 1–5 μm in diameter) and structures (curved, tubular sheath-like, segmented, and mat-like filaments), similar to the Fe-oxidizing bacteria (FeOB) living in modern and ancient hydrothermal vent fields. A previous study revealed that quartz-barite vein swarms were subseafloor channels of low-temperature, silica-rich, diffusive hydrothermal vents in the earliest Cambrian, which contributed silica to the deposition of the overlying bedded chert of the Yurtus Formation. In this context, this study suggests that the putative filamentous FeOB preserved in the quartz veins might have thrived in the low-temperature, silica- and Fe(II)-rich hydrothermal vent channels in subseafloor mixing zones and were rapidly fossilized by subsequent higher-temperature, silica-rich hydrothermal fluids in response to waning and waxing fluctuations of diffuse hydrothermal venting. In view of the occurrence in a relatively stable passive continental margin shelf environment in Tarim Block, the silica-rich submarine hydrothermal vent system may represent a new and important geological niche favorable for FeOB colonization, which is different from their traditional habitats reported in hydrothermal vent systems at oceanic spreading centers or volcanic seamounts. Thus, these newly recognized microfossils offer a new clue to explore the biological signatures and habitat diversity of microorganisms on Earth and beyond.

Carbonaceous Compression Fossils of Macroscopic Benthic Phototrophs Found From Marinoan Cryogenian NeoProterozoic South China

The survival of benthic macroscopic phototrophs on a Neoproterozoic snowball Earth

Authors:

Ye et al

Abstract:

The greatest ice ages in Earth's history occurred during the 654–635 Ma Marinoan glaciation, when glaciers reached tropical oceans and our planet approached a snowball Earth condition. Paleontological and genomic data suggest that several eukaryotic groups must have survived the Marinoan glaciation. But their fossil record is scarce and limited to microbes, whose ecological and physiological ranges are poorly constrained, thus hampering a full understanding of how and where eukaryotic life—particularly macroscopic phototrophs—survived this snowball Earth. Here we report carbonaceous compression fossils from the Marinoan-age Nantuo Formation in South China. These fossils are preserved in thin black shales sandwiched between glacial diamictites deposited in inner shelf environments of the mid-latitudinal Yangtze block. Some of these fossils are interpreted as benthic macroalgae. Thus, the Marinoan glaciation must have been punctuated by episodes of open waters where habitable benthic substrates were available in the photic zone and along the coast of mid-latitudinal continents. Such open waters may have been the refugia where macroscopic phototrophs survived the Marinoan glaciation and subsequently diversified in the early Ediacaran Period.

Cambrian Exoplosion Substrate Adaptations of Sessile Benthic Animals

Substrate adaptations of sessile benthic metazoans during the cambrian radiation

Authors:

Kloss et al

Abstract:

Many marine benthic metazoans must stabilize themselves upon the seafloor for survival, and as a result their morphologies are controlled in part by local substrate conditions. The Agronomic Revolution (AR), spurred by increasing vertical bioturbation during the Ediacaran—Cambrian transition, permanently altered the nature of shallow marine substrate conditions and led to a major shift in adaptive strategies among benthic metazoans. These ecological and evolutionary changes, known as the Cambrian Substrate Revolution (CSR), are generally understood from observations of benthic metazoan fossils across the Ediacaran/Cambrian boundary, but the timing and geographic extent of this transition are less well known. This analysis attempts to constrain the temporal and spatial pattern of the AR and CSR by performing a global-scale paleoecological analysis of the adaptive strategies of benthic fauna living during the Cambrian. This analysis focused on Burgess Shale-type (BST) faunas because of their exceptional preservation, and was conducted through direct observation of fossil specimens, analysis of data compiled from the Paleobiology Database, and literature review. From these analyses, faunal groups are assigned a metric, the Substrate Adaptability Index (SAI), that relates the overall affinity the fauna demonstrates toward either Proterozoic-style (SAI=0) or Phanerozoic-style (SAI= 1) substrate conditions. The results of this analysis demonstrate that most early and middle Cambrian faunas were mixtures of Phanerozoic- and Proterozoic-style adaptive strategists, suggesting that Proterozoic-style substrates were still influential in controlling adaptive strategies in marine environments until at least that time. This is further supported by ichnofabric analysis of many of these localities, where overall bioturbation levels are exceedingly low, indicating a lack of mixed-layer development and the prevalence of firm Proterozoic-style substrates well into the Cambrian.

More Information About the Hettangian Jurassic/Post Triassic-Jurassic Mass Extinction Sponge Bob World

Andean sponges reveal long-term benthic ecosystem shifts following the end-Triassic mass extinction

Authors:

Ritterbush et al

Abstract:

Thick cherts and cherty dolomites in the basal Jurassic Aramachay Formation of Peru preserve a thriving continental shelf community dominated by siliceous sponges that followed the end-Triassic collapse of metazoan-rich carbonate accumulation. Similar Hettangian and Sineumurian deposits from Nevada, U.S.A., Austria, and Morocco suggest that an Early Jurassic siliceous sponge takeover was a widespread phenomenon that persisted for ~ 2 m.y. until metazoan-driven carbonate sedimentation recovered. The post-extinction dominance of siliceous sponges likely resulted from the confluence of metazoan carbonate reef collapse (removal of incumbents) and geochemical conditions that fostered the success of the siliceous sponge-dominated ecosystem. Simple mass balance calculations suggest the siliceous sponge takeover was likely permitted by an increased silica flux as a consequence of weathering Central Atlantic Magmatic Province (CAMP) basalts. The CAMP basalts alone could supply all the silica needed to sustain the sponge takeover, although contributions were also likely from increased hot-climate weathering of other silicates and possible reductions in dissolved silica demand by radiolarians. Detailed sedimentological, fossil, and microfacies analyses were conducted at six field sites across a shallow shelf system recorded in the central Peruvian Andes (Yauli Dome), focusing on the metazoan contribution to sedimentation. Sedimentary structures at all six sites demonstrated on-shelf deposition, similar to the underlying upper Triassic Chambará Formation (in contrast to the black shale-rich facies of the Aramachay Formation in other areas of Peru). Examination of up to 147 m of cherty dolomite from the Aramachay Formation revealed a siliceous sponge-dominated ecosystem, including sponge body fossils, compressed in situ sponge materials, and abundant transported spiculite sediments. Siliceous sponges, mostly demosponges and rare hexactinellids, account for the chert lithology and apparently dominated the local ecology for approximately two million years. The role of metazoan biocalcifiers in sediment production and ecological structure was profoundly reduced compared to the under- and overlying formations, representing a clear ecological state shift from pre-extinction carbonate to post-extinction siliceous dominated ecosystems before the carbonate system recovered ~ 2 m.y. after the extinction.

Evidence of Oxygenated Marine Bottom Waters at the NeoArchean/PaleoProterozoic Boundary?!?!

Petrology And Geochemistry Of The Wangjiazhuang Banded Iron Formation And Associated Supracrustal Rocks From The Wutai Greenstone Belt In The North China Craton: Implications For Their Origin And Tectonic Setting

Authors:

Wang et al

Abstract:

The Wutai greenstone belt (WGB) is one of the most extensively studied greenstone belts in China. Together with the Hengshan and Fuping complexes, these three associations compose the central segment of the Trans-North China Orogen (TNCO) in the North China Craton (NCC). The Wangjiazhuang banded iron formation (BIF) is located in the bottom of the Jingangku Formation of the WGB. The associated supracrustal rocks consist of meta-basalts (amphibolites), meta-felsic volcanic rocks (leptynite) and metapelites (mica schist), which have experienced amphibolite-facies metamorphism. Amphibolites are commonly intercalated with the BIF. SIMS zircon U-Pb analyses on amphibolites suggest that the Wangjiazhuang BIF was formed at ca. 2543 ± 4 Ma. Combined with most Neoarchean Algoma-type BIFs in the NCC, these features indicate that a significant tectothermal event of the NCC have occurred at ∼2.5 Ga. Mineral assemblages of the Wangjiazhuang BIF are composed of quartz, magnetite, amphibole, and minor garnet, pyrite and calcite. The precursor deposits of this BIF were likely ferric-oxyhydroxides, fine-grained carbonate oozes, silicate phases rich in Al-Ca-Mg-Fe and amorphous silica. The appearance of garnet and ferro-pargasite, high concentrations of Al2O3, HFSEs, Sc, and positive correlations among Al2O3, TiO2, HFSEs and REE indicate that there was a significant terrigenous input. Even so, the Wangjiazhuang BIF samples display distinctively seawater-like REE + Y profiles, characterized by positive La and Y anomalies and HREE enrichment relative to LREE in PAAS-normalized REE diagrams. Consistently positive Eu anomalies are also observed, which are typically from high-T hydrothermal fluids. In addition, the true negative Ce anomalies recorded in the Wangjiazhuang BIF might indicate the onset of bottom-water oxidation at the Archean-Proterozoic boundary, at least in restricted basins. Amphibolites have geochemical affinity with both MORB- and arc-like components, and the trace element characteristics of leptynites are also consistent with a subduction zone signature. These features suggest that the Wangjiazhuang BIF was deposited in a back-arc basin. Oceanic subduction, coupled with contemporary depleted mantle upwelling related to back-arc basin extension, can account for the typical interaction between these two components.

First Glimpse at Lower Jurassic Benthic Paleodiversity

First glimpse into Lower Jurassic deep-sea biodiversity: in situ diversification and resilience against extinction

Authors:

Thuy et al

Abstract:

Owing to the assumed lack of deep-sea macrofossils older than the Late Cretaceous, very little is known about the geological history of deep-sea communities, and most inference-based hypotheses argue for repeated recolonizations of the deep sea from shelf habitats following major palaeoceanographic perturbations. We present a fossil deep-sea assemblage of echinoderms, gastropods, brachiopods and ostracods, from the Early Jurassic of the Glasenbach Gorge, Austria, which includes the oldest known representatives of a number of extant deep-sea groups, and thus implies that in situ diversification, in contrast to immigration from shelf habitats, played a much greater role in shaping modern deep-sea biodiversity than previously thought. A comparison with coeval shelf assemblages reveals that, at least in some of the analysed groups, significantly more extant families/superfamilies have endured in the deep sea since the Early Jurassic than in the shelf seas, which suggests that deep-sea biota are more resilient against extinction than shallow-water ones. In addition, a number of extant deep-sea families/superfamilies found in the Glasenbach assemblage lack post-Jurassic shelf occurrences, implying that if there was a complete extinction of the deep-sea fauna followed by replacement from the shelf, it must have happened before the Late Jurassic.

The Benthic Ecology Biodiversity Response to the Abrupt End of the Ice Age

Response of deep-sea biodiversity to abrupt deglacial and Holocene climate changes in the North Atlantic Ocean

Authors:

Yasuhara et al

Abstract:

Aim

Little is known about how marine biodiversity responds to oceanographic and climatic changes over the decadal to centennial time-scales which are most relevant for predicted climate changes due to greenhouse gas forcing. This paper aims to reveal decadal–centennial scale deep-sea biodiversity dynamics for the last 20,000 years and then explore potential environmental drivers.

Location

The North Atlantic Ocean.

Methods

We investigated deep-sea benthic microfossil records to reveal biodiversity dynamics and subsequently applied comprehensive ecological modelling to test possible environmental factors (i.e. surface productivity, seasonality of productivity or deepwater circulation related to bottom-water temperature) that may have influenced deep-sea biodiversity over these time-scales.
Results

Deep-sea biodiversity changed synchronously with stadial–interstadial climate changes over the last 20,000 years across a large area of the North Atlantic in both ostracod crustaceans and foraminiferan protozoa (in spite of their different dispersal abilities). Species diversity rapidly increased during abrupt stadial events during the last deglacial and the Holocene interglacial periods. These include the well-known Heinrich 1, the Younger Dryas and the 8.2 ka events when the strength of Atlantic Meridional Overturning Circulation (AMOC) decreased. There is also evidence for quasi-cyclic changes in biodiversity at a c. 1500-year periodicity, consistent with the well-known ‘1500-year climatic cycle’. Statistical analyses revealed that AMOC variability (probably specifically the variability in AMOC-driven bottom-water temperature) is correlated with deep-sea biodiversity.

Main conclusions

Our finding of a significant AMOC–diversity relationship may indicate pervasive control of the diversity of deep-sea benthic species by rapidly changing climate, specifically bottom-water temperature, over decadal to centennial time-scales. Our results, based on highly resolved fossil records, may portend pervasive, synchronous and sudden ecosystem responses to human-induced changes to climate and ocean circulation in this century.

How the Cambrian Explosion Diversified in the Benthic in Different Climate Zones

Diachronous Increase in Early Cambrian Ichnofossil Size and Benthic Faunal Activity in Different Climatic Regions

Authors:

Mochizuki et al

Abstract:

In order to clarify the pattern of diversification and processes of biological activity during the Cambrian radiation, ichnofossils were comparatively studied in the early Cambrian sections of Newfoundland, South China and western Mongolia. Special attention was paid to size distributions of the most common ichnogenus, Planolites, and the densities of all the observed ichnofossils that preserve animal activity as expressed by bedding plane bioturbation indices (BPBI).

From the Fortune Head section in Newfoundland, a clear size increase in the ichnogenus Planolites is confirmed from the Treptichnus pedum Zone to the overlying Rusophycus avalonensis Zone. The BPBI also shows much stronger biological activity in the R. avalonensis Zone than in the T. pedum Zone. In Meishucun, South China and Gobi-Altai, Mongolia, however, a variety of Planolites sizes had already appeared in the T. pedum Zone, and the BPBI's on some bedding surfaces of the T. pedum Zone are already comparable to those in the R. avalonensis Zone in Newfoundland. In the earliest Cambrian, diversification and increase in the biological activity of the benthic fauna were diachronous in the wide geographic scale, starting earlier at lower latitudes (South China and western Mongolia) than at higher latitudes (Newfoundland), reflecting differences in the onset of Cambrian benthic animal activity under different climatic conditions.

Anoxia, High Temperatures Effected Benthic Biotic Recovery During Scythian Triassic

High temperature and low oxygen perturbations drive contrasting benthic recovery dynamics following the end-Permian mass extinction

Authors:

Pietsch et al

Abstract:

The end-Permian mass extinction event was the greatest loss of biodiversity ever experienced on the planet. The event is thought to have been triggered by the initiation of the volcanic eruptions of the Siberian Traps. The five million year recovery interval that followed the extinction event was strongly influenced by the environmental effects of sustained volcanic eruptions including extreme temperature events and persistent global and regional oxygen minimum zones. The effects of these environmental perturbations on the paleoecological recovery of the benthic marine fauna were studied in two depositional units from the Southwestern United States representing two substages during the Early Triassic recovery. The Smithian Sinbad Limestone was influenced by high sea surface temperatures and contains a relatively high diversity fauna that exhibits extremely small body size. Gastropods that lived in this environment were size-limited, a possible result of metabolic stress due to extreme temperatures. These microgastropods were able to become dominate components of the benthic fauna by occupying niche space vacated by other taxa that were excluded by high temperatures. The Spathian Virgin Limestone shows evidence for low oxygen conditions. The resulting low diversity benthic fauna had a more ecologically complex community structure than the Smithian Sinbad Limestone including the occupation of epifaunal tiering space by crinoids. As the prevalence of aerobic facies increased through time, diversity, body size, and the complexity of faunal interactions also increased suggesting that low oxygen conditions were the limiting factor for the benthic recovery in that region. The differences in diversity and community structure between the two units highlight the importance of environmental and temporal differences in driving the recovery patterns of the benthic fauna following the extinction event. High temperature events and low oxygen conditions restricted the benthic fauna in different ways but both contributed to the delay in recovery from the end-Permian mass extinction.

More Trace Fossil Evidence of Animals in the Ediacaran From South China

Interactions between Ediacaran animals and microbial mats: Insights from Lamonte trevallis, a new trace fossil from the Dengying Formation of South China

Authors:

Meyer et al

Abstract:

A new ichnogenus and ichnospecies, Lamonte trevallis, is formally described from the Shibantan Member limestone of the upper Ediacaran Dengying Formation, Yangtze Gorges area, South China. It is characterized by horizontal tunnels connected with short vertical burrows and surface trails. The horizontal burrows are elliptical or bilobed in transverse cross-section, preserved in full relief, and filled with carbonate intraclasts, micrites, as well as calcite and silica cements. They occur exclusively in silty, crinkled, and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats; no burrows have been found in intraclastic layers adjacent to the microlaminated layers. The vertical traces are filled with the same material as the burrows, but they typically project through the crinkled microlaminae and are exposed on the bedding surface. The surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs. The burrow infill has δ18Ocarb and δ13Ccarb values distinct from, but intermediate between, microlaminated and intraclastic layers, consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements, intraclasts, and micrites. Bedding plane bioturbation intensity (20–40%)—measured as percentage of bedding plane area covered by L. trevallis traces—is comparable to similar measurements in pre-trilobite Cambrian carbonates. The exclusive occurrence of L. trevallis within microbial mats may have both taphonomic and ecological significance. These mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows, and they may have also facilitated early diagenetic cementation of burrow infill, thus facilitating burrow preservation. The close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources. The trace makers of L. trevallis were better able to utilize the resources around them than many other Ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late Ediacaran oceans at the dawn of the agronomic revolution.

Students of Marine Mass Extinctions Take Note: Biotic Recovery of Hypoxic Benthic Environments

Organism-Sediment Interactions Govern Post-Hypoxia Recovery of Ecosystem Functioning

Authors:

1. Carl Van Colen (a)
2. Francesca Rossi (b,c)
3. Francesc Montserrat (b)
4. Maria G. I. Andersson (b)
5. Britta Gribsholt (b)
6. Peter M. J. Herman (b)
7. Steven Degraer (a,d)
8. Magda Vincx (a)
9. Tom Ysebaert (b,e)
10. Jack J. Middelburg (b,f)

Affiliations:

a. Department of Biology, Marine Biology Section, Ghent University, Ghent, Belgium

b. Netherlands Institute for Sea Research (NIOZ-Yerseke), Yerseke, The Netherlands

c. Ecologie des systèmes marins côtiers (Ecosysm) UMR 5119 CNRS-Université Montpellier 2-IRD-Ifremer Place Eugène Bataillon, Université Montpellier II, Case 093, F-34095 Montpellier, France

d. Management Unit of the of the North Sea Mathematical Model, Marine Ecosystem Management Section, Royal Belgian Institute of Natural Sciences, Brussels, Belgium

e. Wageningen University, Institute for Marine Resources & Ecosystem Studies, Yerseke, The Netherlands

f. Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands

Abstract:

Hypoxia represents one of the major causes of biodiversity and ecosystem functioning loss for coastal waters. Since eutrophication-induced hypoxic events are becoming increasingly frequent and intense, understanding the response of ecosystems to hypoxia is of primary importance to understand and predict the stability of ecosystem functioning. Such ecological stability may greatly depend on the recovery patterns of communities and the return time of the system properties associated to these patterns. Here, we have examined how the reassembly of a benthic community contributed to the recovery of ecosystem functioning following experimentally-induced hypoxia in a tidal flat. We demonstrate that organism-sediment interactions that depend on organism size and relate to mobility traits and sediment reworking capacities are generally more important than recovering species richness to set the return time of the measured sediment processes and properties. Specifically, increasing macrofauna bioturbation potential during community reassembly significantly contributed to the recovery of sediment processes and properties such as denitrification, bedload sediment transport, primary production and deep pore water ammonium concentration. Such bioturbation potential was due to the replacement of the small-sized organisms that recolonised at early stages by large-sized bioturbating organisms, which had a disproportionately stronger influence on sediment. This study suggests that the complete recovery of organism-sediment interactions is a necessary condition for ecosystem functioning recovery, and that such process requires long periods after disturbance due to the slow growth of juveniles into adult stages involved in these interactions. Consequently, repeated episodes of disturbance at intervals smaller than the time needed for the system to fully recover organism-sediment interactions may greatly impair the resilience of ecosystem functioning.