Peta J. Mudie

Latest Pleistocene—Holocene paleoceanographic trends on the continental margin of eastern Canada: Foraminiferal, dinoflagellate and pollen evidence

Micropaleontological studies were made of cores from four shelf basins on the eastern Canadian Margin: Emerald and Canso basins on the Scotian Shelf (44°–46° N), Notre Dame Channel, Newfoundland Shelf (50° N) and Cartwright Saddle, Labrador Shelf (55°). Events were correlated using a combination of14C dates and pollen stratigraphies. Surface- and bottom-water changes were compared on the basis of dinoflagellates and benthic foraminifera, respectively. The results indicate significant paleoceanographic shifts along a north—south gradient both prior to and during the Holocene. Distinct Late Pleistocene—Holocene paleoceanographic events were distinguished in the Emerald, Canso and Notre Dame basins; these events are less obvious in Cartwright Saddle which is in deeper water and further off-shore. Pleistocene glaciomarine sediments in all basins contain a fauna dominated byElphidium excavatum f.clavata; dinoflagellates and pollen are rare or absent. The widespreadElphidium fauna probably reflects turbid glacial meltwater and/or a permanent ice shelf cover from 20,000-10,000 yrs BP. The Notre Dame core also penetrates older sediment with an outer Labrador Current fauna which may represent a late Wisconsinian interstade at about 23,000 yrs BP. From 7,000–10,000 yrs BP a cold water fauna occurred which is similar to modern outer Labrador Current faunas. From about 5000–7000 yrs BP, a warm interval is indicated by a relatively warm-water calcareous benthonic foraminiferal fauna and increased representation of typical Gulf Stream dinoflagellates. The most recent change occurred in the last 2000 years with an abrupt cooling associated with stronger flow of the arctic inner Labrador Current. This cooling event is marked by an increase in arctic dinoflagellates and by an exclusively agglutinated benthonic foraminiferal fauna at two sites (Canso and Notre Dame). These Holocene paleoceanographic changes are not clearly seen in the benthic fauna of the deep northern basin (Cartwright Saddle) although dinoflagellate data at this site indicate that surface-water changes have occurred that are similar to those found in shallower basins. Shifts in the zonal position of the Gulf Stream and changes in the relative mass transports of the West Greenland and Labrador currents are mechanisms which may account for the paleoceanographic events. The glacial—interstadial—glacial sequence recorded in the Notre Dame Channel, in conjunction with other theories on glacial triggering mechanisms, provides biostratigraphic evidence which suggests the onset of a glacial stage in the near future.

Biostratigraphy and late Cenozoic paleoceanography of the Arctic Ocean: Foraminiferal, lithostratigraphic, and isotopic evidence

Detailed studies of benthonic foraminifera, stable isotopes, and lithofacies in cores from the southeastern Alpha Ridge, central Arctic Ocean, reveal some new aspects of Arctic Ocean paleoceanography. High ratios of benthonic to planktonic foraminifera are found in most of the Quaternary sediment units, and ratios of 1:1 appear to characterize the Arctic deep-water sediments. Benthonic foraminifera in the carbonate mud unit M show a succession of calcareous species reflecting increased influx of Norwegian Sea bottom water to the Arctic Ocean during the past 0.4 m.y. Foraminiferal and lithological data indicate less-uniform sedimentation during a warmer interval from 0.4 to 0.6 Ma, when most of the silty lutite unit L was deposited at the CESAR site. Lower Pleistocene units J to I contain less limestone and more dolomite, and they contain a uniform faunal assemblage with low numbers of calcareous foraminifera. Upper Pliocene units H to AB contain rare limestone and relatively large amounts of do-lomite and quartz sand. Middle to upper Pliocene units AB to A3 are marked by abundant sand-sized ferromanganese-coated particles, which in many cases have a silt nucleus; hence, much of the coarse sand in these units does not indicate increased ice rafting. The Pliocene sediments mostly contain a low-diversity assemblage of agglutinated foraminifera, but a mixed calcareous/arenaceous fauna occurs in a short interval above the Matuyama-Gauss boundary (2.4 Ma). Stable-isotopic curves occur within sequences which broadly correspond to stages 1-9 of the global record; below stage 9, the record is discontinuous. Strong vertical mixing apparently prevailed during most of the Pliocene and early Pleistocene, then decreased during the past 0.4 m.y. owing to damping by a perennial ice cover. Isotopic and foraminiferal data, however, suggest that an interval of perennial sea ice also occurred during the late Pliocene at the time of the earliest glacial event recorded in the North Atlantic.

Palynological records of red tide-producing species in Canada: past trends and implications for the future

Abstract Increases in ‘red tides’ and other harmful algal blooms (HABs) during the past 50 yr on both the Atlantic and Pacific coasts of Canada suggest that global-scale factors, such as climate change and increased international shipping trade, are the driving forces. Because the historical record is too short to understand the long-term dynamics of HABs, the Holocene history of harmful phytoplankton species was examined using ultra-high resolution studies (annual to decadal scale) of dinoflagellate cysts as a proxy for ‘red tide’ production. Paleoecological transfer functions were then applied to the cyst assemblage data to determine correlations with changes in sea surface temperature and salinity. Pacific records were obtained from varved marine sediments in Saanich Inlet, British Columbia, and in the Santa Barbara Basin off California. Comparison of annual cyst production and historical plankton data provides cyst:theca ratios from which the magnitude of past bloom size can be evaluated. The 10 500-yr Pacific record clearly shows that the largest blooms correspond to cysts of Protoceratium reticulatum and Gonyaulax spinifera during the early Holocene. Sporadic blooms of potentially toxic Alexandrium spp., Lingulodinium polyedrum and Gymnodinium spp. also occurred from ca. 7000 to 5000 yr BP and more frequently from ca. 2000 to 3000 yr BP. Individual Holocene blooms were up to 10 times larger than in the historical record but they almost always occurred sequentially, without overlap of ‘red tide’ species. In pre-historical times, the bloom cycles started and stopped abruptly in 10 yr or less, and they persisted for about 100–1000 yr. In contrast, the variability and near-concurrence of species blooms in the modern (past 60 yr) record is unmatched in the past, and suggests disequilibrium of the natural ecosystem structure. Atlantic records from La Have and Emerald basins on the Scotian Shelf are less precise because bioturbation limits time resolution to ca. 25 yr. However, cyst abundances of cf. Alexandrium , Protoceratium reticulatum , Gonyaulax spinifera and Lingulodinium polyedrum were also an order of magnitude larger in the early Holocene, where they correspond to a summer sea surface warming of 2–5°C. Lesser peaks also appear during the past 2000 yr where they apparently correspond to a slight increase in winter temperature. There is no evidence of much lower salinity that would support stronger stratification. The similarity of pre-industrial age cyst records of ‘red tide’ histories in the oceanographically different Pacific and Atlantic regions of Canada indicates that climate change (including surface temperature and storminess) is the main driving force stimulating blooms. This implies that HABs will reoccur regardless of efforts to limit spreading. However, reduced pollution may decrease the HAB diversity, thereby stabilizing the population dynamics and increasing the predictability of bloom occurrences.

Deltas south of the Bosphorus Strait record persistent Black Sea outflow to the Marmara Sea since ∼10 ka

At the southern exit of the Bosphorus Strait in the northeastern Marmara Sea, high-resolution seismic profiles reveal two lobate, progradational delta lobes in modern water depths of V40^65 m. The younger delta was active from V10 to 9 ka based on radiocarbon dates of equivalent prodelta deposits and the elevation of its topset-to-foreset transition. The topset-to-foreset transition climbs in the seaward direction because the delta prograded into a rising sea. Low abundances of marine fauna and flora in the 10^9-ka interval support a deltaic interpretation. There are no rivers in the area that could have fed the delta; instead, all evidence points to the strait itself as the source of sediment and water. When this outflow was strongest (V10.6^6.0 ka), sapropels accumulated in basinal areas of both the Aegean and Marmara seas. Benthic foraminiferal and dinoflagellate cyst data from contemporary deposits elsewhere in the Marmara Sea point to the continual presence through the Holocene of a surface layer of brackish water that we ascribe to this same outflow from the Black Sea through the Bosphorus Strait. By V9.1^8.5 ka, two-layer flow developed in the Bosphorus Strait as global sea level continued to rise, and the sediment supply to the younger delta was cut off because the outflowing Black Sea water ceased to be in contact with the floor of the strait. The older delta lobe lies below a prominent lowstand unconformity and is tentatively interpreted to have formed from V29.5 to 23.5 ka (oxygen-isotopic stage 3) when the Marmara Sea stood at V355 m and a second sapropel accumulated in deep basinal areas. Crown Copyright ? 2002 Elsevier Science B.V. All rights reserved.

A 340,000 year record of ice rafting, palaeoclimatic fluctuations, and shelf-crossing glacial advances in the southwestern Labrador Sea

Orphan Basin, southwestern Labrador Sea, is a strategic site for the study of Quaternary palaeoceanography and palaeoclimate. A 31.45-m-long piston core (MD95-2025) was raised from 2925-m-depth at 49°47.645′N, 46°41.851′W, just beyond the seaward limit of stacked debris-flow tongues derived from the Northeast Newfoundland Shelf. The core extends to oxygen isotopic stage 9 (∼340,000 years), and includes 13 prominent ice-rafted layers (Heinrich events H1–H13), many of which are characterized by abundant detrital Palaeozoic limestone and dolomite. Warm peaks in sea-surface temperature (SST) show poor correlation with accentuated ice rafting, except for 20–60 ka (H3–H5) when the terminations of meltwater pulses (δ18O minima) lagged warm peaks in SST by ∼1000 years, and peaks in ice rafting either coincided with peaks in SST (H4, H5), or lagged warmer peaks in SST by ∼500 years (H3). These lags are attributed to the delayed response of ice sheets (e.g., iceberg and meltwater production rates) to palaeoceanographic and palaeoclimatic forcing factors (e.g., incursions of the warm North Atlantic Drift into the Labrador Sea; orbital-induced changes in insolation). The remarkable covariance between SST and ice rafting from 20–60 ka is inconsistent with models for ice-stream surging through Hudson Strait [Marshall, S.J. and G.K.C. Clarke, 1997. A continuum mixture model of ice stream thermomechanics in the Laurentide Ice Sheet 2: application to the Hudson Strait ice stream. J. Geophys. Res., B102, 20615–20637], and instead suggests that regional changes in ocean circulation played an important role in destabilizing icesheets. Heinrich layers H1, H3–H6, H9, H11, and H13 formed during times of sharply decreasing δ18O values (i.e., ice sheet melting). Heinrich layers H2, H7 and H12 formed at transitions from interglacial/interstadial to glacial stages, coincident with both cool SST and low fluxes of detrital carbonate. They may represent the initiation of calving as growing ice sheets readvanced to coastal areas of the Labrador Sea and Baffin Bay. Carbonate-poor H8 and H10 developed during interglacial stages 5 and 7, and may have been derived mainly from Greenland like the modern ice-rafted sediments of the Labrador Sea.

Late quaternary pollen transport processes, western North Atlantic: Data from box models, cross-margin and N-S transects

Abstract Surface pollen assemblages in coastal and neritic sediments of the western North Atlantic compare well with eastern North American vegetation zones, and late Quaternary pollen in marginal marine sediments clearly correlate with changes in terrestrial vegetation and paleoclimates. In contrast, offshore assemblages are strongly affected by differential adaptation of pollen to long distance transport by wind and water. Marine pollen transport processes were studied by measuring air and water inputs to a coast-shelf box model, and by study of surface samples from cross-margin transects in three different climatic and oceanographic regions at approximately 38°, 45° and 55°N latitude. The box model shows that aerial transport is the main process by which pollen moves across the continental margin off Nova Scotia. Two clear seabed distribution patterns were found: Betula, Quercus , and herb pollen decrease rapidly offshore in abundance (grains per cubic centimetre) and in relative abundance (percentage); Pinus and Picea have abundance peaks on the continental margin, but percentages increase further offshore. Distributions of the main pollen and spore taxa were compared for late Wisconsinan glacial (oxygen isotopic stage 2, 12–28 ka), terminal Pleistocene (10–12 ka) and Holocene sediments at 5 continental margin and 3 deep-sea sites. The largest changes were found in percentages of Pinus, Picea , and herb pollen during the late Wisconsinan glacial and terminal Pleistocene intervals at subpolar latitudes. These data can be related to shifts in paleo-vegetation, -winds and -hydrology that accompany global climate change.

Oceanic pollen transport and pollen:dinocyst ratios as markers of late Cenozoic sea level change and sediment transport

Abstract Palynological studies of late Cenozoic cores from nine sites show large peaks in the ratio of pollen and spores to dinocysts (P:D) which reflect major increases in terrigenous sediment influx to the North Atlantic Ocean. Under normal pelagic conditions in the North Atlantic, i.e., in the absence of ice rafting or mass wasting, P:D in oceanic sediments is low, usually

Pliocene paleoclimatic reconstruction using dinoflagellate cysts: Comparison of methods

The application of quantitative and semiquantitative methods to assemblage data from dinoflagellate cysts shows potential for interpreting past environments, both in terms of paleotemperature estimates and in recognizing water masses and circulation patterns. Estimates of winter sea-surface temperature (WSST) were produced by using the Impagidinium Index (II) method, and by applying a winter-temperature transfer function (TFw). Estimates of summer sea-surface temperature (SSST) were produced by using a summer-temperature transfer function (TFs), two methods based on a temperature-distribution chart (ACT and ACTpo), and a method based on the ratio of gonyaulacoid:protoperidinioid specimens (G:P). WSST estimates from the II and TFw methods are in close agreement except where Impagidinium species are sparse. SSST estimates from TFs are more variable. The value of the G:P ratio for the Pliocene data in this paper is limited by the apparent sparsity of protoperidinioids, which results in monotonous SSST estimates of 14–26°C. The ACT methods show two biases for the Pliocene data set: taxonomic substitution may force ‘matches’ yielding incorrect temperature estimates, and the method is highly sensitive to the end-points of species distributions. Dinocyst assemblage data were applied to reconstruct Pliocene sea-surface temperatures between 3.5−2.5 Ma from DSDP Hole 552A, and ODP Holes 646B and 642B, which are presently located beneath cold and cool-temperate waters north of 56°N. Our initial results suggest that at 3.0 Ma, WSSTs were a few degrees C warmer than the present and that there was a somewhat reduced north-south temperature gradient. For all three sites, it is likely that SSSTs were also warmer, but by an unknown, perhaps large, amount. Past oceanic circulation in the North Atlantic was probably different from the present.

THE MARMARA SEA GATEWAY SINCE ~16 KY BP: NON-CATASTROPHIC CAUSES OF PALEOCEANOGRAPHIC EVENTS IN THE BLACK SEA AT 8.4 AND 7.15 KY BP

The Late Quaternary history of connection of the Black Sea to the Eastern Mediterranean has been intensely debated. Ryan, Pitman and coworkers advocate two pulses of outflow from the Black Sea to the world ocean at ~16–14.7 ky BP and ~11–10 ky BP. From ~14.7–11 ky BP and from ~10–8.4 ky BP, they suggest that the level of the Black Sea fell to ~ -100 m. At 8.4 ky BP, they further claim that a catastrophic flood occurred in a geological instant, refilling the Black Sea with saline waters from the Mediterranean. In contrast, we continue to gather evidence from seismic profiles and dated cores in the Marmara Sea which demonstrate conclusively that the proposed flood did not occur. Instead, the Black Sea has been at or above the Bosphorus sill depth and flowing into the world ocean unabated since ~10.5 ky BP. This conclusion is based on continuous Holocene water-column stratification (leading to sapropel deposition in the Marmara Sea and the Aegean Sea), proxy indicators of sea-surface salinity, and migration of endemic species across the Bosphorus in both directions whenever appropriate hydrographic conditions existed in the strait. The two pulses of outflow documented by Ryan, Pitman and coworkers find support in our data, and we have modified our earlier interpretations so that these pulses now coincide with the development of mid-shelf deltas: \Delta 2 (16–14.7 ky BP) and \Delta 1 (10.5–9 ky BP) at the southern end of the Bosphorus Strait. However, continued Black Sea outflow after 9 ky BP prevented the northward advection of Mediterranean water and the entry of open-marine species into the Black Sea for more than 1000 years. Sufficient Mediterranean water to change the Sr-isotopic composition of slope and shelf water masses was not available until ~8.4 ky BP (along with the first arrival of many varieties of marine fauna and flora), whereas euryhaline molluscs did not successfully populate the Black Sea shelves until ~7.15 ky BP. Instead of relying on catastrophic events, we recognize a slow, progressive reconnection of the Black Sea to the world ocean, accompanied by significant time lags.

Palynostratigraphy and chronostratigraphy of Baffin Bay deep sea cores: Climatostratigraphic implications

Abstract Palynostratigraphic considerations and 14C dates (AMS; accelerator mass spectrometry) on foraminifera samples from piston cores suggest sedimentation rates as high as ca. 8–11 cm/ka in deep Baffin Bay during the Late Pleistocene. Throughout this interval Baffin Bay experiences rigorous conditions and probably the extension of a dense sea-ice cover unfavourable to phytoplanktonic productivity: the dinocyst microflora indicates only brief episodes of higher productivity related to Arctic conditions and to moderately low salinites (ca. 30–31ℵ). The abundance of reworked pre-Quaternary palynomorphs in the deposits is interpreted as a response to glacial and glacio-marine activity in the northernmost areas surrounding Baffin Bay. The dinocyst stratigraphy spanning approximately over the last ice age (ca. 100 ka) reveals that Baffin Bay constituted a confined basin, isolated from the North Atlantic Ocean, prior to the present “Interglacial”.