Francine M.G. McCarthy

A Comparison of Postglacial Arcellacean (Thecamoebian) and Pollen Succession in Atlantic Canada, Illustrating the Potential of Arcellaceans for Paleoclimatic Reconstruction

Cores dating back to deglaciation were taken from three lakes in Atlantic Canada and analyzed for arcellaceans and pollen. Paleotemperatures and paleo-precipitation were calculated from the pollen data using transfer functions. A sudden warming is recorded by the pollen around 10,000 years B.P., followed by a general warming to the mid Holocene Hypsithermal, then by a decrease in temperature and increase in effective precipitation to the present. The three lakes, two in western Newfoundland and one in eastern Nova Scotia, contain similar late glacial (13-10 ka), early Holocene (10-8 ka), mid Holocene (8-4 ka), and late Holocene (4-0 ka) arcellacean assemblages. Immediately following retreat of the ice sheets, Centropyxis aculeata, Centropyxis constricta, Difflugia oblonga, Difflugia urceolata, and Difflugia corona were common. The latter part of the late glacial is characterized by sparse assemblages dominated by C. aculeata. The arcellacean record thus suggests a climatic reversal in Atlantic Canada between 11,500 and 10,000 years B.P., analogous to the Younger Dryas, although this is not recorded by the pollen. Species diversity increased sharply at the beginning of the Holocene, and D. oblonga is the dominant taxon in early Holocene sediments. Difflugia oblonga remained common through the mid Holocene, but percentages of C. aculeata were very low, and Pontigulasia compressa and Difflugia bacillifera peaked in abundance during the Hypsithermal. The late Holocene is characterized by a resurgence in C. aculeata at the expense of other taxa. The increase in Heleopera sphagni and Nebella collaris since 5,000 years B.P. at the two sites in southwestern Newfoundland reflects paludification in response to increased precipitation since the Hypsithermal. Because the changes in arcellacean assemblages are regionally synchronous in all three lakes and coincide with climatically driven vegetational successions indicated by the pollen record, arcellaceans appear to respond to climatic change, and thus may be useful paleoecological and paleolimnological indicators. With their quicker generation time, these protists may be better suited than pollen to recording short-lived phenomena, like the mid-Holocene Hypsithermal and the Younger Dryas reversal.

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

Marine palynology : potentials for onshore-offshore correlation of Pleistocene-Holocene records : marine studies

A review of marine pollen-spore distributions reveals regional variations in primary transport pathways. Fluvial transport prevails on the mountainous margins of the eastern Pacific and off major river deltas, including Arctic estuaries. Elsewhere, wind and sea ice are the main transport agents, and pollen concentration corresponds to dust influx. Redeposition of Quaternary palynomorphs is also important near emergent continental ice sheet centres where fine-grained sediment is being eroded. Pre-Quaternary palynomorphs can indicate sources of ice-rafted debris. Preservation and transport of pollen in marine sediments is not well understood. Laboratory processing with acetolysis shows damage of bisaccate grains, and copepod feeding experiments show some pollen damage of grains within the faecal pellet membranes. A multi-box model shows the relative importance of rivers, wind and ocean currents in pollen transport to shelves of Atlantic Canada: most pollen is wind-transported, but large storms may indirectly increase influx. In the Arctic, sea ice scouring and sediment transport are important in addition to northeasterly winds. These glacial processes would impact a third of the planet during glaciations. Pleistocene cores from NW Atlantic and Pacific Oceans show that glacial stage transport differed from that during Holocene and other interglacials because glacioeustatic lowstands exposed the continental shelves, and wind strength and direction changed following ice sheet growth. Pollen influxes and ice-volume records show variable leads and lags of palaeometerological events at glacial/interglacial boundaries, with a major decline in terrigenous organics after ∼0.4 Ma (MIS 13-11).

Dry Climate Disconnected the Laurentian Great Lakes

Recent studies have produced a new understanding of the hydrological history of North Americas Great Lakes, showing that water levels fell several meters below lake basin outlets during an early postglacial dry climate in the Holocene (younger than 10,000 radiocarbon years, or about 11,500 calibrated or calendar years before present (B.P.)). Water levels in the Huron basin, for example, fell more than 20 meters below the basin overflow outlet between about 7900 and 7500 radiocarbon (about 8770–8290 calibrated) years B.P. Outlet rivers, including the Niagara River, presently falling 99 meters from Lake Erie to Lake Ontario (and hence Niagara Falls), ran dry. This newly recognized phase of low lake levels in a dry climate provides a case study for evaluating the sensitivity of the Great Lakes to current and future climate change.

12 600 years of lake level changes, changing sills, ephemeral lakes and Niagara Gorge erosion in the Niagara Peninsula and Eastern Lake Erie basin

Over the last 12 600 years, lake levels in the eastern Lake Erie basin have fluctuated dramatically, causing major changes in drainage patterns, flooding and draining ephemeral Lake Wainfleet several times and widening and narrowing the Niagara Gorge as the erosive effects of Niagara Falls waxed and waned. The control sill for Lake Erie levels was at first the Fort Erie/Buffalo sill, before the Lyell/Johnson sill in Niagara Falls took over due to isostatic rebound. This sill, in time, was eventually eroded by the recession of Niagara Falls and the Fort Erie/Buffalo sill regained control. The environmental picture is complicated by catastrophic outbursts from glacial Lake Agassiz and Lake Barlow-Ojibway, changes in outlet routes, isostatic rebound and climatic changes over the Great Lakes basins. Today, the flow of water into Lake Erie from the streams and rivers surrounding it only accounts for about 13% of the flow out of it, therefore, the importance of flow from the Upper Great Lakes, specifically the flow from Lake Huron, has a great effect on Lake Erie levels. While the changing control sills, Lyell/Johnson and Buffalo/Fort Erie would affect Lake Erie levels, overall they are mostly input driven by the amount of waters received from the Upper Great Lakes. Since Lake Eries water level changes are so closely tied to Lake Hurons water level changes we have decided to use names assigned to Lake Huron such as the two Mattawa highstands and three Stanley lowstands rather than inflict a whole new set of names on the public. While the duration of each high and lowstand in Erie and Huron may not always be the same, they always happen within the same time frame. The datum elevations used for Lake Huron (175.8 m) and Lake Erie (173.3 m) are historically recorded averages. The Lake Erie levels proposed in this paper reflect Lake Hurons effects on Lake Erie and the levels occuring at the eastern end of the Erie Basin throughout the last 12 600 years. All dates in this paper are uncorrected 14 C dates unless the date was obtained from shells, then the date has been corrected for hard-water effects. Also, all heights are given as modern day elevations and are not adjusted for isostatic rebound.

Evolution of lakes in the Huron basin: Deglaciation to present

Water bodies, ancestral to the present lakes including Lake Huron, first appeared in the southern Great Lakes basin about 15,500 14 C years (18,800 cal years) BP during the oscillatory northward retreat of the last (Laurentide) ice sheet from its maximum position south of the Great Lakes watershed. Glacial lakes, impounded by a retreating ice margin on their northern shores, were continuously present after 13,000 14 C (15,340 cal) BP for 3000 14 C (3900 cal) years. Drainage routings varied in time through the Erie and Michigan basins to the Mississippi River system, a probable source for colonizing aquatic organisms, then to the Ontario basin, and finally northeastward to the Ottawa River valley via the isostatically-depressed North Bay outlet by 10,000 14 C (11,470 cal) BP. Water levels were generally low between 10,000 and 7500 14 C (11,470 and 8300 cal) BP and may have risen several tens of metres for short periods due to overflow of meltwater from upstream subglacial reservoirs or from glacial lakes impounded by residual ice in the Hudson Bay watershed. About 8000 14 C (8890 cal) BP glacial runoff bypassed the Great Lakes, and Huron basin waters descended into hydrologic closure under the influence of the early Holocene dry climate. With increasing precipitation and water supply about 7500 14 C (8300 cal) BP the Huron water body again overflowed its North Bay outlet. Differential isostatic uplift (fastest to the north-northeast) raised this outlet and lake level relative to the rest of the basin. The lake finally overflowed southern outlets at Chicago and Port Huron-Sarnia by 5000 14 C (5760 cal) BP (during the Nipissing highstand). Enhanced erosion of the latter outlet and continued differential uplift of the basin led to the present configuration of Lake Huron and Georgian Bay.

The palynological record of terrigenous flux to the deep sea: late Pliocene–Recent examples from 41°N in the abyssal Atlantic and Pacific oceans

Abstract Sediments of late Pliocene to Recent age from two abyssal sites at 41°N latitude (ODP Site 898 in the eastern Atlantic Ocean and ODP Site 1179 in the western Pacific Ocean) generally contain sparse palynomorph assemblages dominated by oxidation-resistant gonyaulacacean dinoflagellate cysts. Some samples at both sites had unexpectedly high palynomorph concentrations, high P:D (pollen:dinoflagellate cyst) and low G:P (gonyaulacacean:protoperidiniacean) values. These samples record an increase in terrigenous flux and in the rate of sedimentation. Sedimentological data from ODP Hole 898A support the interpretation of pollen and protoperidiniacean dinoflagellate cyst-rich calcareous sandy muds as distal turbidites. We suggest that palynological analysis is more accurate than sediment grain size in distinguishing distal turbidites from pelagites. Similar palynological assemblages in biosiliceous oozes at Site 1179 have a different origin. The close correlation of peaks in total palynomorph concentration with anomalous preservation of protoperidiniacean dinoflagellate cysts as well as biogenic calcium carbonate 1 km below the modern CCD suggests a link between terrigenous flux and sea surface productivity. The increased flux of biogenic particles (including planktonic foraminiferal tests) driven by the increased availability of continentally derived limiting nutrients in oceanic waters appears mainly responsible for the increased sedimentation rate which allows oxidation-susceptible dinoflagellate cysts and dissolution-susceptible calcareous microfossils to be preserved. The ages of these palynomorph-rich calcareous intervals at this and several other nearby sites in the western North Pacific suggest that the resulting sequestration of both organic and inorganic carbon affected the greenhouse effect sufficiently to drive late Cenozoic global cooling.

Chronology of Eocene–Miocene sequences on the New Jersey shallow shelf: Implications for regional, interregional, and global correlations

Integrated Ocean Drilling Program Expedition 313 continuously cored and logged latest Eocene to early-middle Miocene sequences at three sites (M27, M28, and M29) on the inner-middle continental shelf offshore New Jersey, providing an opportunity to evaluate the ages, global correlations, and significance of sequence boundaries. We provide a chronology for these sequences using integrated strontium isotopic stratigraphy and biostratigraphy (primarily calcareous nannoplankton, diatoms, and dinocysts [dinoflagellate cysts]). Despite challenges posed by shallow-water sediments, age resolution is typically ±0.5 m.y. and in many sequences is as good as ±0.25 m.y. Three Oligocene sequences were sampled at Site M27 on sequence bottomsets. Fifteen early to early-middle Miocene sequences were dated at Sites M27, M28, and M29 across clinothems in topsets, foresets (where the sequences are thickest), and bottomsets. A few sequences have coarse (∼1 m.y.) or little age constraint due to barren zones; we constrain the age estimates of these less well dated sequences by applying the principle of superposition, i.e., sediments above sequence boundaries in any site are younger than the sediments below the sequence boundaries at other sites. Our age control provides constraints on the timing of deposition in the clinothem; sequences on the topsets are generally the youngest in the clinothem, whereas the bottomsets generally are the oldest. The greatest amount of time is represented on foresets, although we have no evidence for a correlative conformity. Our chronology provides a baseline for regional and interregional correlations and sea-level reconstructions: (1) we correlate a major increase in sedimentation rate precisely with the timing of the middle Miocene climate changes associated with the development of a permanent East Antarctic Ice Sheet; and (2) the timing of sequence boundaries matches the deep-sea oxygen isotopic record, implicating glacioeustasy as a major driver for forming sequence boundaries.

SYNCHRONOUS PALYNOLOGICAL CHANGES IN EARLY PLEISTOCENE SEDIMENTS OFF NEW JERSEY AND IBERIA, AND A POSSIBLE PALEOCEANOGRAPHIC EXPLANATION

Palynomorphs record the establishment of modern conditions in the subtropical North Atlantic during the early Pleistocene. Prior to ~1.4 Ma, muds on both the New Jersey shelf and the Iberia Abyssal Plain contained relatively few terrestrial palynomorphs, and had a dinocyst flora rich in Operculodinium israelianum and other dinocyst taxa recording warmer surface waters than at present (e.g., Tectatodinium pellitum, Lingulodinium machaerophorum, and Polysphaeridium zoharyi). Over a span of ~250 ka, this palynological assemblage was succeeded by one rich in pollen and with a dinocyst flora similar to the “modern” flora, i.e. rich in Operculodinium centrocarpum, Bitectatodinium tepikiense, Spiniferites spp. (predominantly S. ramosus), and Brigantedinium spp. (predominantly B. simplex). The synchronous palynological changes in such different geological settings in the eastern and western subtropical North Atlantic are attributed to global climatic deterioration and the expansion of ice sheets in the northern hemisphere. Climatic cooling increased the velocity of the Gulf Stream and other surface currents in the subtropical gyre, causing the gyre to contract and pull away from the continents. Glacioeustatically lowered sea levels also exposed a large percentage of the continental shelf areas, and together with other bathymetric highs like the Charleston Bump, deflected the gyre boundary currents (like the Gulf Stream) offshore. Consequently, surface waters of polar origin were able to penetrate between the warm waters of the gyre and the North American continent north of Cape Hatteras in the west, and Iberia in the east, around 1.4 Ma. This paleoceanographic change increased the area of “neritic” sedimentation at mid latitudes in the North Atlantic, allowing greater terrestrial influx beyond the shelfbreak.