The Palaeocene/Eocene thermal maximum, ~55 million years ago, was a brief period of widespread, extreme climatic warming1, 2, 3, that was associated with massive atmospheric greenhouse gas input4. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition5. We show that sea surface temperatures near the North Pole increased from ~18 °C to over 23 °C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations6, but the absolute polar temperatures that we derive before, during and after the event are more than 10 °C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms—perhaps polar stratospheric clouds7 or hurricane-induced ocean mixing8—to amplify early Palaeogene polar temperatures.

/pdf/subtropical-arctic-ocean-temperatures-during-the-palaeocene-1iu2p4jtlb.pdf

Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum

Ichnology is the study of traces created in the substrate by living organisms. This is the first book to systematically cover basic concepts and applications in both paleobiology and sedimentology, bridging the gap between the two main facets of the field. It emphasizes the importance of understanding ecologic controls on benthic fauna distribution and the role of burrowing organisms in changing their environments. A detailed analysis of the ichnology of a range of depositional environments is presented using examples from the Precambrian to the recent, and the use of trace fossils in facies analysis and sequence stratigraphy is discussed. The potential for biogenic structures to provide valuable information and solve problems in a wide range of fields is also highlighted. An invaluable resource for researchers and graduate students in paleontology, sedimentology and sequence stratigraphy, this book will also be of interest to industry professionals working in petroleum geoscience.

Ichnology: Organism-Substrate Interactions in Space and Time

Phylogeography posits that the sequence of speciation events within a clade should parallel the geographic migration and isolation of members of the clade through time. The primary historical features that govern migration and allopatry in land plants are changes in physical geography (e.g., oceans, mountains, and deserts) and in climate (e.g., moisture, temperature, and day length), features that are often interrelated. If we assume that living genera retain physiological stability through time, much as they retain the morphological features that allow their identification, then these environmental features of the geologic past may be used to test phylogeographic hypotheses of living genera based on phylogenetic analysis. The history of the climatic and geographic features of the Tertiary of the Northern Hemisphere agrees with many phylogenetically based phylogeographic hypotheses of living angiosperm genera but indicates that some hypotheses require reanalysis. While the parallel comparison of phylogene...

https://www.jstor.org/stable/10.1086/323880

The Use of Geological and Paleontological Evidence in Evaluating Plant Phylogeographic Hypotheses in the Northern Hemisphere Tertiary

A major contribution to our initial understanding of the origin, history and biogeography of the present-day arctic flora was made by Eric Hulten in his landmark book Outline of the History of Arctic and Boreal Biota during the Quarternary Period, published in 1937. Here we review recent molecular and fossil evidence that has tested some of Hulten's proposals. There is now excellent fossil, molecular and phytogeographical evidence to support Hulten's proposal that Beringia was a major northern refugium for arctic plants throughout the Quaternary. In contrast, most molecular evidence fails to support his proposal that contemporary east and west Atlantic populations of circumarctic and amphi-Atlantic species have been separated throughout the Quaternary. In fact, populations of these species from opposite sides of the Atlantic are normally genetically very similar, thus the North Atlantic does not appear to have been a strong barrier to their dispersal during the Quaternary. Hulten made no detailed proposals on mechanisms of speciation in the Arctic; however, molecular studies have confirmed that many arctic plants are allopolyploid, and some of them most probably originated during the Holocene. Recurrent formation of polyploids from differentiated diploid or more low-ploid populations provides one explanation for the intriguing taxonomic complexity of the arctic flora, also noted by Hulten. In addition, population fragmentation during glacial periods may have lead to the formation of new sibling species at the diploid level. Despite the progress made since Hulten wrote his book, there remain large gaps in our knowledge of the history of the arctic flora, especially about the origins of the founding stocks of this flora which first appeared in the Arctic at the end of the Pliocene (approximately 3 Ma). Comprehensive analyses of the molecular phylogeography of arctic taxa and their relatives together with detailed fossil studies are required to fill these gaps.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-294X.2003.01731.x

History and evolution of the arctic flora: in the footsteps of Eric Hulten

Tetrachloroethene (PCE) and trichloroethene (TCE) are ideal solvents for numerous applications, and their widespread use makes them prominent groundwater pollutants. Even more troubling, natural biotic and abiotic processes acting on these solvents lead to the accumulation of toxic intermediates (such as dichloroethenes) and carcinogenic intermediates (such as vinyl chloride). Vinyl chloride was found in at least 496 of the 1,430 National Priorities List sites identified by the US Environmental Protection Agency, and its precursors PCE and TCE are present in at least 771 and 852 of these sites, respectively. Here we describe an unusual, strictly anaerobic bacterium that destroys dichloroethenes and vinyl chloride as part of its energy metabolism, generating environmentally benign products (biomass, ethene and inorganic chloride). This organism might be useful for cleaning contaminated subsurface environments and restoring drinking-water reservoirs.

Detoxification of vinyl chloride to ethene coupled to growth of an anaerobic bacterium.

The first opening of the Bering Strait was an important palaeogeographical and biogeographical event for marine and terrestrial biotas in Asia and North America1,2,3, and an oceanographic event of global importance4,5,6. This event, however, has never been precisely dated, so it has not been accurately incorporated into models of global biogeography and oceanography. A recent find of the bivalve mollusc Astarte in southern Alaska is a clear signal that the strait had opened by at least the Late Miocene or earliest Pliocene epochs, because this genus otherwise dwelled only in the Arctic and North Atlantic oceans at that time1,2. Here we show that marine diatoms with Astarte are correlative with subzone b of the Neodenticula kamtschatica zone of the North Pacific diatom biochronology, yielding an age range of 4.8–5.5 Myr (refs 7, 8). Stratigraphic information suggests that this may be a minimum age range for the strait's first opening, which evidently occurred between 4.8 and 7.3–7.4 Myr ago. Our results contrast with past studies9,10,11,12,13 that suggested an age of 3.1–4.1 Myr for the initial opening of the Bering Strait.

Evidence for an early opening of the Bering Strait

A refined age for the earliest opening of Bering Strait

New evidence for the age of Bering Strait

Late Paleocene Arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios

The Pliocene interchange of North Pacific and North Atlantic marine faunas via the Arctic Ocean was long thought to have been a single episode of faunal exchange between the northern oceans that took place as soon as the Bering Strait first opened. New evidence implies that there were two northern migration events instead of one, and that the second phase of migration was much later than the first. The migration of Atlantic-Arctic mollusks into the Bering Sea and North Pacific when the Bering Strait first opened at 4.8–5.5 Ma constituted the initial phase of this interchange, but the abrupt appearance of North Pacific mollusks in the North Atlantic at 3.6 Ma postdated the first opening of the Bering Strait by 1.2–1.9 m.y. This second phase of trans-Arctic migration was also coeval with shoaling of the Central American seaway between North and South America. This late Pliocene trans-Arctic migration of North Pacific mollusks is evidence for the reversal of marine flow to northward through the Bering Strait, which was one consequence of the reorganization of Northern Hemisphere ocean circulation caused by substantial closure of the Central American seaway. This inferred causal link between the histories of the Beringian and Panamanian ocean gateways is in agreement with ocean circulation models.

Louie Marincovich

Papers

Evidence for an early opening of the Bering Strait

A refined age for the earliest opening of Bering Strait

New evidence for the age of Bering Strait

Late Paleocene Arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios

Central American paleogeography controlled Pliocene Arctic Ocean molluscan migrations