R. Mark Leckie

Global cooling during the eocene-oligocene climate transition.

About 34 million years ago, Earths climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earths temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple ocean localities and show that the high-latitude temperature decrease was substantial and heterogeneous. High-latitude (45 degrees to 70 degrees in both hemispheres) temperatures before the climate transition were ∼20°C and cooled an average of ∼5°C. Our results, combined with ocean and ice-sheet model simulations and benthic oxygen isotope records, indicate that Northern Hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time.

Timing and paleoceanography of oceanic dysoxia/anoxia in the late Barremian to early Aptian (Early Cretaceous)

Normal marine deposition in the early Aptian was interrupted by an episode of ocean-wide dysoxia/anoxia. This event is recorded by the occurrence of organic carbon-rich sediments in land sections from Europe and Deep Sea Drilling Project (DSDP)/Ocean Drilling Program (ODP) sites in the North and South Atlantic, Indian and Pacific Ocean Basins. To elucidate the origin, and spatial and temporal relationships of these carbonaceous sediments, we have conducted an integrated biostratigraphic, lithostratigraphic and geochemical investigation of fourteen sections from a range of geographic and oceanographic settings

Paleoecology of Mid-Cretaceous planktonic foraminifera; a comparison of open ocean and epicontinental sea assemblages

Although our knowledge of living planktonic foraminifera is limited, useful paleoecologic information can be obtained from ancient assemblages. During the mid-Cretaceous, as today, the simple, inflated morphotypes inhabited the nearsurface waters while the flatter, keeled forms probably occupied deeper habitats. Three faunal groups are proposed, an Epicontinental Sea Fauna (ESF) characterized by species of Gubkinella, Guembelitria and Heterohelix, an open marine Shallow Water Fauna (SWF) composed primarily of species of Hedbergella and Globigerinelloides, among others, and finally an open marine Deep Water Fauna (DWF) represented by species of Planomalina, Rotalipora and Praeglobotruncana (keeled taxa). Open ocean assemblages of DSDP Sites 545 and 547 are numerically dominated by species of the SWF in the >63-,um size fraction while the ESF comprises about 5% of the assemblages, and the biostratigraphically important DWF generally comprises less than 2%. These assemblages demonstrate remarkable stratigraphic consistency. In contrast to open ocean assemblages, epicontinental sea assemblages of the Vocontian Basin are characterized by loss of the DWF with decreasing water depth and an increase in the proportion of the ESF. The ESF:SWF ratio also becomes increasingly variable with decreasing water depth. Upwelling also has pronounced effects on the composition of planktonic assemblages as suggested by an increase in the proportion of the ESF, interpreted to include opportunistic species.

The Cretaceous-Tertiary boundary cocktail: Chicxulub impact triggers margin collapse and extensive sediment gravity flows

A distinctive mixture of reworked microfossils, impact-derived materials, and lithic fragments occurs in sediments at the Cretaceous-Tertiary boundary in the basinal Gulf of Mexico and Caribbean. We have named this mixture the Cretaceous-Tertiary boundary “cocktail.” Lithologic and paleontologic evidence suggests that the cocktail was deposited by giant sediment gravity flows, apparently triggered by the collapse of continental margins around the Gulf of Mexico as a result of the Chicxulub impact. As most microfossils in the gravity-flow units are reworked, biostratigraphy provides only maximum ages. Recognition of the cocktail is a reliable way to identify Cretaceous-Tertiary boundary deposits in the basinal Gulf of Mexico and Caribbean.

A paleoceanographic model for the early evolutionary history of planktonic foraminifera

The first major radiations of planktonic foraminifera occurred during the mid-Cretaceous. However, this period of great diversification was interrupted by two intervals of pronounced paleoceanographic/paleoecologic change, one during the latest Aptian-early Albian and a second associated with the Cenomanian-Turonian boudary. Both of these times corresponded with widespread organic carbon burial during intervals commonly referred to as Oceanic Anoxic Events (OAE) 1 and 2, respectively. This synthesis focuses on the evolutionary history of Aptian-early Cenomanian planktonic foraminifera and the relationship with OAE 1. Dynamic paleoceanographic changes controlled the course of planktonic foraminiferal evolution during the mid-Cretaceous. Heightened plate tectonic activity, a major long-term rise of global sea level and an overall increase of global temperatures characterized Aptian-Albian time. As proposed here, the evolutionary history of Aptian-early Cenomanian planktonic foraminifera was influenced most strongly by changes in the density structure and stability of the upper water column via changes in the sites and rates of water mass production through time, and perhaps by subtle changes in oceanic productivity (including trophic structure) and shifts in productivity centers with rising sea level. The creation and growth of epicontinental seas played a major role in regional climate change, water mass production and water column structure. Epicontinental seas were also an important factor in creating vast new niche space and increased biotic diversity for many marine organisms. The amplified seasonality and instability of epicontinental seas resulted in habitation of the upper water column by morphologically simple, eurytopic planktonic foraminifera. Several new species of epicontinental sea dwelling planktonic foraminifera appeared during the mid-Cretaceous. However, much of the diversification of morphologic form took place in oceanic areas during times of oceanic stability and upper water column stratification during mid-to late Aptian and late Albian time. A decline in diversity and return to simple morphotypes occurred when oceanic stability was disrupted and the upper water column was poorly stratified during latest Aptian-early Albian time.

ACTIVE-LEARNING METHODS TO IMPROVE STUDENT PERFORMANCE AND SCIENTIFIC INTEREST IN A LARGE INTRODUCTORY OCEANOGRAPHY COURSE

Teaching methods that are often recommended to improve the learning environment in college science courses include cooperative learning, adding inquiry-based activities to traditional lectures, and engaging students in projects or investigations. Two questions often surround these efforts: 1) can these methods be used in large classes; and 2) how do we know that they are increasing student learning? At the University of Massachusetts, we have transformed the environment of a large-enrollment oceanography course (600 students) by modifying lectures to include cooperative learning via interactive in-class exercises and directed discussion. Assessments were redesigned as “two-stage” exams with a significant collaborative component. Results of student surveys, course evaluations, and exam performance demonstrate that learning of the subject under these conditions has improved. Student achievement shows measurable and statistically significant increases in information recall, analytical skills, and quantitative reasoning. There is evidence from both student surveys and student interview comments that for the majority of students, the course increased their interest in science — a difficult effect to achieve with this population.

Late Oligocene–early Miocene glacial record of the Ross Sea, Antarctica: Evidence from DSDP Site 270

Foraminifera from Deep Sea Drilling Project Site 270, Ross Sea, Antarctica, are used to trace an early phase of glaciation during the late Oligocene–early Miocene. The central Ross Sea underwent significant bathymetric and oceanographic evolution with the inception of glaciomarine sedimentation, resulting in the sequential development of four contrasting foraminiferal populations (assemblage zones). Gradual climatic change in the Ross Sector during latest Paleogene-early Neogene time culminated in major ice build-up by the late early Miocene. Conclusions derived from our microfaunal studies reaffirm climatic and oceanographic trends interpreted from oxygen-isotope data for sub-Antarctic deep sea sites north of the Ross. Sea. Intensification of glaciation within the Ross Sea area may be responsible for the increase in production of Antarctic Bottom Water and associated development of widespread early Neogene deep-sea hiatuses reported from lower latitude regions.

The record of Ontong Java Plateau: Main results of ODP Leg 130

The drilling campaign of ODP Leg 130 on Ontong Java Plateau resulted in the recovery of complete Neogene sections at several depths, providing materials for detailed biostratigraphic and paleoceanographic studies in the western equatorial Pacific. The acquisition of extensive logging records and high-resolution physical-property data allow detailed correlation from hole to hole and from site to site and provide the basis for a paleoceanographic interpretation of acoustic reflectors. We drilled 16 holes at 5 sites on the north-eastern flank of the plateau (Sites 803 through 807). All sites are close to the equator, at water depths ranging from 2,500 m to 3,900 m. Sites 803 and 807 penetrated into basement (26 m and 149 m, respectively). The K/T boundary was recovered at both of these sites. Neogene sedimentation rates decrease with depth, as expected, but this decrease is much greater than calculated from carbonate content, under the assumption that carbonate dissolution is the sole cause of the decrease. At any one site, sedimentation rates vary by a factor of more than two, with a striking maximum in the latest Miocene to early Pliocene, and strong minima in late early to early middle Miocene and in the Pleistocene. Many acoustic reflectors correlate between sites, within the limits of stratigraphic resolution. This suggests paleoceanographic events as a cause, generating changes in physical properties of sediments at the time of deposition. Many of the reflectors occur at carbonate reduction events (CREs). Some apparently are the product of diagenetic enhancement of property changes, as, for example, within the ooze/chalk transition (which is diachronous). The interval corresponding to the Cretaceous/Tertiary (K/T) transition in the area is characterized by the presence of a deep CCD. The sequence at one site is calcareous; that at the other, is not. The fact that the two K/T sections recovered occur in sequences with major hiatuses suggests special conditions for preservation during the transition. We propose early cementation caused by high silicate concentrations in an ocean with greatly reduced productivity. The basalt cored at Sites 803 and 807 is predominantly aphyric to sparsely olivine or plagioclase phyric; the last flows are Albian to Aptian in age. At Site 807, pillow lavas buried sediments. One very thick flow (∼28 m) was penetrated here, possibly a flood basalt, indicative of massive outpourings on Ontong Java Plateau during the middle Cretaceous.

HIGH-RESOLUTION ESTUARINE SEA LEVEL CYCLES FROM THE LATE CRETACEOUS: AMPLITUDE CONSTRAINTS USING AGGLUTINATED FORAMINIFERA

Agglutinated foraminifera provide high-resolution proxies for relative sea level change in Late Cretaceous coal-bearing strata. Three foraminiferal assemblages are recognized where Trochammina (trochospiral) occurs in abundance with either one of the following: 1) Miliammina (quinqueloculine) associated with carbonaceous shale, interpreted as the marsh; 2) Ammobaculites (uncoiled) and estuarine ostracodes associated with shelly mudstones, interpreted as the central, muddy estuary; and 3) Verneulinoides and Textularia (serial) associated with gray mudstones, interpreted as distal estuary (open bay). The marsh represents 0–1 m water depth and this approximates absolute mean sea level, the central estuary represents 5–8 m water depth, and the distal estuary (open bay) represents water depths of 10 m or greater. Alternations between foraminiferal associations in a 25-m section of the upper middle Turonian Smoky Hollow Member, Straight Cliffs Formation, indicate sea level amplitude changes that ranged from 1–10 meters.

Seeking a better life in the plankton

Foraminifers are single-celled, testate protists with a rich geologic record spanning at least 500 million years of Earths most recent history. Their abundance, diversity, and diagnostic distribution patterns make them very useful to Earth scientists for purposes of relative age determination, correlation from one locality to another, and paleoenvironmental reconstructions. Benthic foraminifers occupy nearly every conceivable marine habitat ranging from coastal salt marshes and estuaries to marginal silled basins and deep-sea trenches. They range from pole to pole and are particularly diverse and abundant in shallow waters of the tropics. Planktic foraminifers have a shorter geologic history that begins ≈180 Ma in the late Early Jurassic. Traditional classification has assigned all of the planktic forms to a single suborder Globigerinina (1). Such a classification scheme implies a monophyletic origin for the planktic foraminifers, although many specialists have long suspected a polyphyletic origin from benthic ancestors.