Richard W. Jordan

A model system approach to biological climate forcing. The example of Emiliania huxleyi

Abstract Particulate inorganic carbon (calcium carbonate mineral) is produced by pelagic calcifying organisms in the upper layers of the open ocean, it sinks to the deep sea, is partly dissolved and partly stored in the geological archive. This phenomenon, known as the carbonate pump, is an important component of the global carbon cycle and exerts a major influence on climate. The amount of carbonate mineral produced depends on the evolutionary and ecological success of calcifying pelagic organisms. The formulation of adequate predictive carbonate pump modules raises the problem that the behaviour of this highly diverse set of organisms needs to be taken into account. To overcome this difficulty, we propose a “model system” approach, whereby a single representative organism, the coccolithophore Emiliania huxleyi , is investigated in detailed interactive experimental and modelling studies. To construct a comprehensive model of the carbonate pump, subsequent research is envisaged on additional representative organisms, but this work is likely to be facilitated by the experience gained with E. huxleyi . The model system approach permits (1) an emphasis on the non-linear character of the fluxes; (2) a focus on the coupling of the carbonate pump with other climatically important phenomena — the organic carbon pump and DMS production; and (3) exploitation of the experimental accessibility of the E. huxleyi system.

Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris

Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic, contain ice-rafted debris (IRD) back to the middle Eocene epoch, prompting recent suggestions that ice appeared in the Arctic about 46 million years (Myr) ago. However, because IRD can be transported by icebergs (derived from land-based ice) and also by sea ice, IRD records are restricted to providing a history of general ice-rafting only. It is critical to differentiate sea ice from glacial (land-based) ice as climate feedback mechanisms vary and global impacts differ between these systems: sea ice directly affects ocean–atmosphere exchanges, whereas land-based ice affects sea level and consequently ocean acidity. An earlier report assumed that sea ice was prevalent in the middle Eocene Arctic on the basis of IRD, and although somewhat preliminary supportive evidence exists, these data are neither comprehensive nor quantified. Here we show the presence of middle Eocene Arctic sea ice from an extraordinary abundance of a group of sea-ice-dependent fossil diatoms (Synedropsis spp.). Analysis of quartz grain textural characteristics further supports sea ice as the dominant transporter of IRD at this time. Together with new information on cosmopolitan diatoms and existing IRD records, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas ∼47.5 Myr ago, followed ∼0.5 Myr later by the onset of seasonally paced sea-ice formation in offshore areas of the central Arctic. Our data establish a 2-Myr record of sea ice, documenting the transition from a warm, ice-free environment to one dominated by winter sea ice at the start of the middle Eocene climatic cooling phase.

Marine and terrestrial biomarker records for the last 35,000 years at ODP site 658C off NW Africa

Several high-resolution proxy environmental records have been obtained for the last 35 kyr from ODP Hole 658C, a well-studied site ca. 200 km oA Cap Blanc, NW Africa. The collective assessment based on the marine proxies (U K 0 37 SST, contents of TOC and chlorins, Upwelling Radiolarian Index and the percentage of Florisphaera profunda), surprisingly indicates that the last glacial maximum (LGM) was characterized by warmer sea surface temperature (SST), weaker upwelling, and lower marine productivity, compared with the preceding older glacial and subsequent deglaciation periods. Of the terrigenous proxies, the mean grain size of the non-carbonate fraction and the terrigenous alkane content indicate that wind strength and aridity were high. The weaker upwelling at the 658 site during the LGM may have resulted from changes in the strength and direction of the wind systems and/or shifts in the position and geometry of the upwelling cell. # 2000 Elsevier Science Ltd. All rights reserved.

Biodiversity among haptophyte algae

The division Haptophyta is represented only by about 300 extant species showing wide diversity in morphology, biochemistry and ecology. They have a world-wide distribution and are numerically important in phytoplankton populations in nearly all marine environments. Evidence from the geological record shows that they have been the major constituent of calcareous deposits since the Late Triassic and, as they have evolved quickly through time, their coccoliths have always shown wide morphological diversity. In todays oceans they occasionally produce extensive blooms, visible by satellite imagery, which have ecological impact. As a consequence of these blooms the haptophyte algae are now receiving greater attention, as their role in the global sulphur and carbon cycles may influence the worlds climate, and their potential as nuisance bloom algae have implications for commercial fishing and the marine ecosystem. As it is likely that these organisms have always produced such blooms, these effects may have been in operation for the last 200 million years.

A siliceous microfossil view of middle Eocene Arctic paleoenvironments: A window of biosilica production and preservation

Integrated Ocean Drilling Program (IODP) Expedition 302, “The Arctic Coring Expedition” (ACEX), unearthed the most significant find of Paleogene siliceous microfossils in nearly 2 decades. 100 m of early middle Eocene, organic-rich, finely laminated sediments contain abundant marine and freshwater siliceous microfossils allowing intriguing insights into central Arctic paleoenvironments during the start of Cenozoic cooling. Largely endemic assemblages of marine diatoms and ebridians are preserved along with very high abundances of chrysophyte cysts, the endogenously formed resting stage of freshwater algae. An overall brackish environment is invoked, but variations in group dominance suggest episodic changes in salinity, stratification, and trophic status. With the backing of inorganic geochemistry we synthesize the sediment characteristics by hypothesizing an environmental model for the cooccurrence of these diverse siliceous microfossil groups. We also report on initial insights into the composition of some of the laminations, which may help explain the formation of this rich sediment archive.

Eocene silicoflagellate and ebridian paleoceanography in the central Arctic Ocean

The silicoflagellate and ebridian assemblages in early middle Eocene Arctic cores obtained by IODP Expedition 302 (ACEX) were studied in order to decipher the paleoceanography of the upper water column. The assemblages in Lithologic Unit 2 (49.7–45.1 Ma), one of the biosiliceous intervals, were usually endemic as compared to the assemblages that occurred outside of the Arctic Ocean. The presence of these endemic assemblages is probably due to a unique environmental setting, controlled by the degree of mixing between the low-salinity Arctic waters and relatively high salinity waters supplied from outside the Arctic Ocean, such as the Atlantic and possibly the Western Siberian Sea. Using the basin-to-basin fractionation model, the early middle Eocene Arctic Ocean corresponds to an estuarine circulation type, which includes the modern-day Black Sea. The abundant down-core occurrence of ebridians strongly suggests the past presence of low-salinity waters, and may indicate that low oxygen concentrations prevailed in the euphotic layer, on the basis of the ecology of the modern ebridian Hermesinum adriaticum.

TAXONOMY OF THE FOSSIL MARINE DIATOM RESTING SPORE GENUS GONIOTHECIUM EHRENBERG AND ITS ALLIED SPECIES

Taxonomic notes are provided on the genus Goniothecium and its allied groups from Arctic core materials, in addition to a synonymy list, microscope observations and several key references for each species. Moreover, the type material of Goniothecium from the Ehrenberg Collection (no. 1651a and 1651b) in the Museum für Naturkunde, Humboldt Universität, Berlin, was obtained in order to examine the structure of G. rogersii. The extinct genus is characterized by a subrectangular frustule and forming paired frustules connected by two epivalves, which possess interlocking linking spines. The genus presently includes 3 species: G. rogersii Ehrenberg, G. danicum Grunow and G. decoratum Bran. A fourth species, Goniothecium loricatum Fenner is here transferred to Hemiaulus loricatus (Fenner in Schrader et Fenner) Suto comb, nov., based on the valve similarity of genus Hemiaulus. Goniothecium has a long stratigraphic history from the Cretaceous to the Pliocene. Goniothecium rogersii and G. decoratum appeared in the Southern Hemisphere in the late Cretaceous and in the middle Eocene, respectively. From the Oligocene, they spread to the Northern Hemisphere. On the other hand, G. danicum appeared in the North Atlantic and/or Arctic Ocean and spread to the Southern Hemisphere in the Oligocene. The spread (or migration) of Goniothecium species from North to South and vice versa might have been influenced by changes in the thermohaline circulation and ocean current structure across the Eocene/Oligocene boundary. Since diatoms live in the euphotic zone, transportation of living cells over long distances most likely occurs by surface (or intermediate) water currents, however, more resistant resting spores may be laterally advected by bottom water currents.

Taxon lists for studies of modern nannoplankton

Abstract Six studies in this special issue dealt with modern nannoplankton assemblages. In total during these studies 552 samples were analysed and about 180,000 specimens identified, from 152 species. This paper provides a unified list of taxa from these studies, records the presence/absence of each species across the studies and indicates the more common species. Comparison of results indicates a high level of consensus on taxonomy and a high commonality of the floras.

Marine necklace-chain Fragilariaceae (Bacillariophyceae) from Guam, including descriptions of Koernerella and Perideraion, genera nova

Light microscopy (LM) and scanning electron microscopy (SEM) studies of necklace‐chain forming colonial diatoms from benthic habitats in Guam revealed five species. Bleakeleya notata (Grunow in Van Heurck) Round is widespread and well‐known. Asterionella notata var. recticostata Körner has been reported only twice before; we describe the plastids for the first time. On phylogenetic grounds we assign A. notata var. recticostata to a new genus, Koernerella, and emend the description of Bleakeleya. Three new species belonging in a new genus, Perideraion, are described as P. montgomeryi, P. decipiens and P. elongatum. Cultures from single‐cell isolates yielded four gene sequences for three of these taxa. The genera are easy to identify in the LM and SEM. Perideraion differs from Bleakeleya and Koernerella in having two large H‐shaped plastids, as reported for Asterionellopsis and Asteroplanus, and is further distinguished from all these genera by the following character set: a distinct rim around the basal field of circular pores, an apical rimoportula laterally on the valve mantle, pores in the valves that are unlike those in the basal pore field, and absence of apical slits. Although the basal pole attachment and colony morphology seem synapomorphic, molecular evidence suggests that the Bleakeleya‐Koernerella‐Perideraion clade is separate from the Asterionellopsis‐Asteroplanus clade and these five genera do not form one monophyletic group. It remains to be seen whether they are part of a somewhat larger group at the base of the araphid grade or if the genera we studied are truly separate.

An amended terminology for the Parmales (Chrysophyceae)

S. Konno and R. W. Jordan. 2007. An amended terminology for the Parmales (Chrysophyceae). Phycologia 46: 612–616. DOI: 10.2216/07-29.1. Recent studies on Antarctic microplankton have revealed interesting and seemingly overlooked information on the shape and arrangement of the cell wall plates of species belonging to the Triparmaceae (Parmales, Chrysophyceae). In contrast to previous work, it is now known that Tetraparma has four plate types (shield, girdle, ventral and dorsal), suggesting a much closer relation to Triparma. A study of the literature has also provided an opportunity to re-evaluate the plate arrangement in Pentalamina. These revelations have brought about a need to revise the current terminology of the cell wall plates, as well as emendations to the order, family and generic descriptions.