Surface Water Connection Research Articles

Hydrologic connectivity and morphologic variation of oxbow lakes in a pristine alpine fluvial system

The lifespan of oxbow lakes in a meandering system typically exhibits considerable disparity due to the diverse evolutionary processes that lead to their terrestrialization. Although oxbow lakes generally undergo a long-term gradual shrinking trend, their hydrologic connectivity and morphologic variations under variable hydrologic conditions of the river are not well understood. Here we focus on a group of oxbow lakes in a pristine alpine fluvial system in the Qinghai-Tibet Plateau to examine the hydrogeomorphic response of oxbow lakes to a variable hydrologic regime of an active meandering channel. We find that the oxbow lakes are characterized by extensively developed compound forms and connecting “tie” channels and that the lateral migration of the main channel discernably impacts lake morphology and evolution. With increasing discharges in the main channel, the oxbow lakes generally show increases in length under relatively lower flows (RI < 10 years) and more dramatic increases in width under higher flows (RI > 10 years), which collectively lead to their expansion regardless of their hydrologic connectivity. This implies hydrogeomorphic processes other than surface water connection between oxbow lakes and the main channel in adjusting water levels of the lakes. To quantify hydrologic connectivity, we propose a probability-based index and find the overall low hydrologic connectivity of the studied oxbow lakes, owing to the unique paleogeographic setting of the study area. The infrequent but pulsed sedimentation within the lakes and the relatively slow lateral migration of the meandering channel catalyze an inactive floodplain of the study reach.

Campanian-Eocene dinoflagellate cyst biostratigraphy in the Southern Andean foreland basin: Implications for Drake Passage throughflow

The tectonic opening of the Tasmanian Gateway and Drake Passage represented crucial geographic requirements for the Cenozoic development of the Antarctic Circumpolar Current (ACC). Particularly the tectonic complexity of Drake Passage has hampered the exact dating of the opening and deepening phases, and the consequential onset of throughflow of the ACC. One of the obstacles is putting key regional tectonic events, recorded in southern Patagonian sediments, in absolute time. For that purpose, we have collected Campanian-Eocene sediment samples from the Chilean sector of Southern Patagonia. Using U-Pb radiometric dating on zircons and dinoflagellate cyst biostratigraphy, we updated age constraints for the sedimentary formations, and the hiatuses in between. Thick sedimentary packages of shallow-marine and continental sediments were deposited in the foreland basin during the early Campanian, mid-Paleocene, the Paleocene-Eocene boundary interval and the middle Eocene, which represent phases of increased foreland subsidence. We interpret regional sedimentary hiatuses spanning the late Campanian, early-to mid-Paleocene, mid-Eocene and latest Eocene-early Oligocene to indicate times of reduced foreland subsidence, relative to sediment supply. We relate these changes to varying subduction rates and Andean orogeny. Dinoflagellate cyst assemblages suggest that the region was under the influence of the Antarctic-derived waters through the western boundary current of the Subpolar Gyre, developed in the southwest Atlantic Ocean and thus argues for limited throughflow through the Drake Passage until at least the latest Eocene. However, the proliferation of dinoflagellate endemism we record in the southwest Atlantic is coeval with that in the southwest Pacific, and on a species level, dinoflagellate cyst assemblages are the same in these two regions. This suggests that both regions were oceanographically connected throughout the early Paleogene, likely through a shallow opening of a restricted Drake Passage. This implies a continuous surface-water connection between the south Pacific and the South Atlantic throughout the late Cretaceous-early Paleogene.

Two Ocean Pass: An Alternative Hypothesis for the Invasion of Yellowstone Lake by Lake Trout, and Implications for Future Invasions

Preventing the interbasin transfer of aquatic invasive species is a high priority for natural resource managers. Such transfers can be made by humans or can occur by dispersal through connected waterways. A natural surface water connection between the Atlantic and Pacific drainages in North America exists at Two Ocean Pass south of Yellowstone National Park. Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri used this route to cross the Continental Divide and colonize the Yellowstone River from ancestral sources in the Snake River following glacial recession 14,000 bp. Nonnative lake trout Salvelinus namaycush were stocked into lakes in the Snake River headwaters in 1890 and quickly dispersed downstream. Lake trout were discovered in Yellowstone Lake in 1994 and were assumed to have been illegally introduced. Recently, lake trout have demonstrated their ability to move widely through river systems and invade headwater lakes in Glacier National Park. Our objective was to determine if lake trout and other nonnative fish were present in the connected waters near Two Ocean Pass and could thereby colonize the Yellowstone River basin in the past or future. We used environmental DNA (eDNA), electrofishing, and angling to survey for lake trout and other fishes. Yellowstone cutthroat trout were detected at nearly all sites on both sides of the Continental Divide. Lake trout and invasive brook trout S. fontinalis were detected in Pacific Creek near its confluence with the Snake River. We conclude that invasive movements by lake trout from the Snake River over Two Ocean Pass may have resulted in their colonization of Yellowstone Lake. Moreover, Yellowstone Lake may be vulnerable to additional invasions because several other nonnative fish inhabit the upper Snake River. In the future, eDNA collected across smaller spatial intervals in Pacific Creek during flow conditions more conducive to lake trout movement may provide further insight into the extent of non-native fish invasions in this stream.

Albian–Cenomanian calcareous nannofossils from DSDP Site 364 (Kwanza Basin, Angola): Biostratigraphic and paleoceanographic implications for the South Atlantic

The Albian–Cenomanian was an interval of extreme warmth due to greenhouse climatic conditions, as well as significant changes in the paleogeography and paleoceanography of the oceans, which affected the evolution of marine ecosystems on a global scale. This study analyzed the calcareous nannofossil assemblages from 72 samples that were recovered from Site 364 (Kwanza Basin, Angola), which was drilled by the Deep Sea Drilling Project (DSDP) Leg 40. A total of 103 calcareous nannofossil species were recovered, enabling the identification of biozones (CC 8 to CC 10a; or BC 23 to UC 1b/UC 4a) allowing to assign an Albian–Cenomanian interval for the deposition of the studied section. The recovered assemblages have a subtropical-tropical affinity and are indicative of a surface water connection between the Central Atlantic and the South Atlantic oceans, that extends at least as far as offshore Angola. The area sedimentation was predominantly calcareous and pelagic during this interval, with the exception of the basal section, where Albian black shales interbedded with dolomitic and marly limestones were deposited. Throughout the section, high concentrations of TOC and sulfur and the presence of dissolution-susceptible species likely indicate low euxinic conditions for the Kwanza Basin. Dissolution is a significant process for Site 364 in the majority of the studied samples, although not to the point where species richness was severely impacted, as small amounts of dissolution-susceptible taxa were observed. Dissolution showed a marked decrease in intervals in which paleontological and geochemical data indicated an increase in surface water fertility/productivity.

Modeled Postglacial Landscape Evolution at the Southern Margin of the Laurentide Ice Sheet: Hydrological Connection of Uplands Controls the Pace and Style of Fluvial Network Expansion

AbstractLandscapes of the U.S. Central Lowland were repeatedly affected by the Laurentide Ice Sheet. Glacial processes diminished relief and disrupted drainage networks. Deep valleys carved by meltwater were disconnected from the surrounding uplands. The upland area lacking surface water connection to the drainage network is referred to as noncontributing area (NCA). Decreasing fractions of NCA on older surfaces suggest that NCA becomes drained over time. We propose that the integration could occur via (1) capture of NCA as channels propagate into the upland or (2) subsurface or intermittent surface connection of NCA to external drainage networks providing increased discharge to promote channel incision. We refer the two cases as “disconnected” and “connected” since the crucial difference between them is the hydrological connection of the upland to external drainage. We investigate the differences in evolution and morphology of channel networks in low‐relief landscapes under disconnected and connected regimes using numerical simulations. We observe substantially faster rates of erosion and integration of the channel network in the connected case. The connected case also creates longer, more sinuous channels than the disconnected case. Sensitivity tests indicate that hillslope diffusivity has little influence on the evolution and morphology. The fluvial erosion coefficient has significant impact on the rate of evolution, and it influences the morphology to a lesser extent. Our results and a qualitative comparison with landscapes of the glaciated U.S. Central Lowland suggest that connection of NCAs is a potential control on the evolution and morphology of postglacial landscapes.

Patterns and drivers for wetland connections in the Prairie Pothole Region, United States

Ecosystem function in rivers, lakes and coastal waters depends on the functioning of upstream aquatic ecosystems, necessitating an improved understanding of watershed-scale interactions including variable surface-water flows between wetlands and streams. As surface water in the Prairie Pothole Region expands in wet years, surface-water connections occur between many depressional wetlands and streams. Minimal research has explored the spatial patterns and drivers for the abundance of these connections, despite their potential to inform resource management and regulatory programs including the U.S. Clean Water Act. In this study, wetlands were identified that did not intersect the stream network, but were shown with Landsat images (1990–2011) to become merged with the stream network as surface water expanded. Wetlands were found to spill into or consolidate with other wetlands within both small (2–10 wetlands) and large (>100 wetlands) wetland clusters, eventually intersecting a stream channel, most often via a riparian wetland. These surface-water connections occurred over a wide range of wetland distances from streams (averaging 90–1400 m in different ecoregions). Differences in the spatial abundance of wetlands that show a variable surface-water connection to a stream were best explained by smaller wetland-to-wetland distances, greater wetland abundance, and maximum surface-water extent. This analysis demonstrated that wetland arrangement and surface water expansion are important mechanisms for depressional wetlands to connect to streams and provides a first step to understanding the frequency and abundance of these surface-water connections across the Prairie Pothole Region.

Intermittent Surface Water Connectivity: Fill and Spill Vs. Fill and Merge Dynamics

Intermittent surface connectivity can influence aquatic systems, since chemical and biotic movements are often associated with water flow. Although often referred to as fill and spill, wetlands also fill and merge. We examined the effects of these connection types on water levels, ion concentrations, and biotic communities of eight prairie pothole wetlands between 1979 and 2015. Fill and spill caused pulsed surface water connections that were limited to periods following spring snow melt. In contrast, two wetlands connected through fill and merge experienced a nearly continuous, 20-year surface water connection and had completely coincident water levels. Fill and spill led to minimal convergence in dissolved ions and macroinvertebrate composition, while these constituents converged under fill and merge. The primary factor determining differences in response was duration of the surface water connection between wetland pairs. Our findings suggest that investigations into the effects of intermittent surface water connections should not consider these connections generically, but need to address the specific types of connections. In particular, fill and spill promotes external water exports while fill and merge favors internal storage. The behaviors of such intermittent connections will likely be accentuated under a future with more frequent and severe climate extremes.

Role of the geomorphic setting in controlling groundwater–surface water exchanges in riverine wetlands: A case study from two southern Québec rivers (Canada)

There is great interest worldwide to reconnect floodplain wetlands to their rivers. Whilst the surface water connection between rivers and wetlands is fairly well understood, the linkages via groundwater are not well known. In this study, it is hypothesized that the significance of the groundwater pathways between rivers and wetlands is largely determined by the geomorphic setting of the riverine corridor. This was tested by measuring the response of water levels and temperatures in floodplain groundwater and in wetlands to river pulses in two geomorphologically distinct riverine corridors in Southern Québec. In the De la Roche River (DLR; 145 km2), the floodplain is narrow and the alluvial sediments consist of sandy silt (wetland A; abandoned meander) or clayey silt (wetland B; stable floodplain), depending on the location. During within-channel floods, exchanges of water between the river and the floodplain are limited to some bank recharge where the alluvial sediments are permeable, and over-bank storage where the sediments are finer. Water levels in the DLR floodplain wetlands were controlled by a combination of over-bank flow and groundwater discharge from adjacent uplands. In the Matane River (1678 km2), the floodplain substrate is coarser, and the floodplain is wider and has a meandering planform geometry. The response of the Matane River wetland during floods shows storage of water due to a groundwater flood wave. This response of the wetland to within-channel flood pulses could play a role in downstream flood attenuation. In this river, the presence of river infiltration in this floodplain was also illustrated by the warming of floodplain groundwater during flood pulses. This study has shown with three distinct examples how riverine wetlands can be connected to their rivers via either a surface or subsurface pathway depending on the geomorphic setting of the riverine corridor.

APTIAN-ALBIAN PLANKTIC FORAMINIFERA FROM DSDP SITE 364 (OFFSHORE ANGOLA): BIOSTRATIGRAPHY, PALEOECOLOGY, AND PALEOCEANOGRAPHIC SIGNIFICANCE

This work presents a taxonomic, biostratigraphic and paleoecological study of planktic foraminifera recovered from the Aptian–Albian carbonate-dominated succession of Deep Sea Drilling Project (DSDP) Site 364, located in the Kwanza Basin (offshore Angola). Twenty-nine planktic foraminiferal species were identified, enabling the identification of late Aptian–late Albian biozones, from the Hedbergella trocoidea Zone to the Pseudothalmanninella ticinensis Zone. A major unconformity from the latest early–earliest late Albian was identified in core 31, with the Microhedbergella rischi Zone in direct contact with the Pseudothalmanninella ticinensis Zone. The recovered assemblages are characterized by open marine epipelagic dwellers and indicate predominant mesotrophic environmental conditions throughout the studied stratigraphic succession. Aptian planktic foraminiferal assemblages have a tropical/subtropical paleobiogeographic affinity, supporting a surface-water connection between the central proto-Atlantic Ocean and the northern South Atlantic Ocean (north of the Walvis Ridge-Rio Grande Rise) by the late Aptian. Trends in isotopic values for δ 13 C suggest a late Aptian age ( Globigerinelloides algerianus Zone) for the stratigraphic interval from core 42 to ~core 37, where age-diagnostic foraminiferal species are missing. Black shale levels in cores 42–39 are probably the local expression of the “late Aptian anoxic event.”

Large-scale controls on potential respiration and denitrification in riverine floodplains

Restoration measures of deteriorated river ecosystems generally aim at increasing the spatial heterogeneity and connectivity of these systems in order to increase biodiversity and ecosystem stability. While this is believed to benefit overall ecological integrity, consequences of such restoration projects on biogeochemical processes per se (i.e. ecosystem functioning) in fluvial systems are rarely considered. We address these issues by evaluating the characteristics of surface water connection between side arms and the main river channel in a former braided river section and the role and degree of connectivity (i.e. duration of surface water connection) on the sediment biogeochemistry. We hypothesized that potential respiration and denitrification would be controlled by the degree of hydrological connectivity, which was increased after floodplain restoration. We measured potential microbial respiration (SIR) and denitrification (DEA) and compared a degraded floodplain section of the Danube River with a reconnected and restored floodplain in the same river section. Re-establishing surface water connection altered the controls on sediment microbial respiration and denitrification ultimately impacting potential microbial activities. Meta-variables were created to characterize the effects of hydrology, morphology, and the available carbon and nutrient pools on potential microbial processing. Mantel statistics and path analysis were performed and demonstrate a hierarchy where the effects of hydrology on the available substrates and microbial processing are mediated by the morphology of the floodplain. In addition, these processes are highest in the least connected sites. Surface water connection, mediated by morphology regulates the potential denitrification rate and the ratio of N2O to N2 emissions, demonstrating the effects of restoration in floodplain systems.

Extreme variability of water table dynamics in temperate calcareous fens: Implications for biodiversity

AbstractCalcareous fens are minerotrophic peatlands with very high species diversity, and maintenance of the water table is assumed to be a key contributor to this diversity. However, this assumption is based on limited study of fen water table dynamics. Here we monitor water table fluctuation in distributed locations across three calcareous fens differing in hydrogeomorphic setting for three growing seasons. Water table position was extremely variable with absolute ranges of 89, &gt; 100, and &gt; 118 cm in the Riparian, Trough and Basin Fens, respectively, and was controlled by landscape position and weather variability. Areas adjacent to a second‐order stream experienced the least water table fluctuation, while the Basin Fen, at &gt; 75 m from a surface water connection, was very prone to year‐to‐year precipitation differences. Mean and median water table values were found to be poor indicators of biologically relevant hydroperiods. We introduce the term ‘duration of initial growing season saturation’ as a potentially more useful statistic to relate to plant species distribution. Across the studied fens, this duration ranged from 1 to 14 weeks from the start of the growing season. The water table resided below the ground surface for between 0 and 22 weeks of the growing season across the calcareous fens and study period. These findings impart great differences in the development of oxidized rooting depths. Our results demonstrate that there is much more variation in calcareous fen hydrology than previously reported, and this variability has important implications for fen vegetation patterning and management. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Effect of enhanced water exchange on ecosystem functions in backwaters of an urban floodplain

This study evaluated the effects of a controlled surface water connectivity scheme on several backwaters in an urban floodplain within the city limits of Vienna, the Upper Lobau. A phosphorus budget and ecosystem metabolism measurements were used to assess the reaction of two trophically distinct floodplain backwater sections on changed connectivity conditions. The surface water connection led to a reduction of the retention times in the backwater system. The water column nutrient concentrations in the individual backwater sections approached those of the source water body. The significance of these effects, however, depends on the historical and current trophic situation of the respective water bodies. Generally, the surface water connectivity introduced particulate phosphorus export up to 30% increase over the influent loading and dissolved phosphorus up to 14% increase over the influent loading. However, in sections with submersed macrophyte development, which provided enhanced filtering capacities for particulate matter, sediment and phosphorus accumulation rates were increased. At the same time, water transparency increased resulting in a positive feedback supporting further macrophyte development. Based on these findings, the evaluation of restoration measures in urban floodplains needs to consider the spatial and temporal dynamics of nutrients and ecosystem processes such as gross primary production and community respiration to predict long-term development.

Biodiversity in protected coastal wetlands along the west coast of Lake Huron

Lake Huron protected (barrier-protected) wetlands occur within 1 km of the lake, in swales, interdunal ponds, and other shallow depressions. These wetlands are not directly connected via surface water to Lake Huron, although their hydrology is influenced by lake levels. Biodiversity in them has not been well documented. We compiled plant and animal species occurrence data from published and unpublished sources for the U.S. coast of Lake Huron. Many data sources were reports written by the authors and/or by scientists of the Michigan Natural Features Inventory. Species occurrence data were supplemented with data from published wetlands literature and dissertations and theses. We did not do a thorough compilation for Canadian wetlands and only added limited Canadian data from the “Ontario Great Lakes Coastal Wetlands Atlas”. We estimate that total species richness exceeds 1400 species with about an equal number of plants and animals (600–700 species each). We documented the occurrence of 466 macrophytes in Lake Huron’s protected marshes, fens, and swamps and estimated total plant species richness to be &amp;gt; 600. Invertebrate species richness was estimated to be 500–600 with more than half of these being macroinvertebrates (&amp;gt; 0.5 mm) and the remainder being microinvertebrates (&amp;lt; 0.5 mm). Vertebrate species richness was estimated to be &amp;gt; 200 as follows. Fish species richness was estimated to be &amp;lt; 10 because of low oxygen, periodic dry periods, and lack of surface water connection to Lake Huron. Amphibian species richness was estimated to be &amp;gt; 20 with 10 frogs and toads and 7 salamander species documented. Reptile species richness was estimated to be &amp;gt; 20 based on very limited data and published distribution maps with &amp;gt; 10 turtle species and &amp;gt; 10 snake species but no lizards in Lake Huron marshes (although 4–5 lizard species occur on sandy ridges near swale marshes). More than 50 mammal and 80 bird species were estimated to occur in protected wetlands. Occasional additional use by birds and other species combined with the addition of rare species as additional sampling occurs are likely to increase the number of vertebrate species to &amp;gt; 200.

Temporal connectivity in a prairie pothole complex

A number of studies have noted the occurrence of intermittent surface-water connections between depressional wetlands in general and prairie potholes in particular. Yet, the ecological implications of such connections remain largely unexplored. In 1995, we observed spillage into and out of a North Dakota wetland during two field visits. Between May 3 and May 26, there was a positive relationship between specific conductance and water level at this site, suggesting an external source of dissolved ions. We estimated that specific conductance may have increased at the site by as much as 614 μS cm−1 due to spillage from the upslope wetland. Based on a spatial analysis that compared National Wetlands Inventory maps with 1996 color infrared imagery, we estimated that 28% of the area’s wetlands had a temporary surface water connection to at least one other wetland at that time, including one complex of 14 interconnected wetlands. These results indicate that the connectivity observed in 1995 was not confined to the two wetlands nor to that single year. The degree of connectivity we observed would be expected to occur during the wetter portions of the region’s 20-year wet-dry cycle. We hypothesize that intermittent surface-water connections between wetlands occur throughout the prairie pothole region. Given patterns in relief and precipitation, these connections most likely would have occurred in the eastern portion of the prairie pothole region. However, wetland drainage may have altered historical patterns. The implication of these spatial and temporal trends is that surface-water connections between depressional wetlands should be viewed as a probability event that has some distribution over time and space. We refer to connections that are impermanent, temporally discontinuous, or sporadic as temporal connectivity. The most intriguing feature of these temporary connections may be that they could affect biodiversity or population dynamics through transport of individuals or reproductive bodies. Research is needed to determine whether these connections actually cause these biological effects and to characterize the distribution and effects of this phenomenon.

Nd- and Pb-isotope time series from Atlantic ferromanganese crusts: implications for changes in provenance and paleocirculation over the last 8 Myr

High-resolution Nd- and Pb-isotope time series for the last 8 Myr are reported for four Atlantic ferromanganese crusts, dated by 10Be/ 9Be chronology. These are compared to new high-resolution and high-precision Pb-isotope time series and recently published Nd-isotope time series for two previously studied crusts from the NW Atlantic Ocean. These records allow a more detailed examination of Atlantic deepwater variability over the time period of intensification of Northern Hemisphere Glaciation (NHG). Changes in the Pb-isotope time series started after 3 Ma, but were most dramatic over the last 1.8 Myr, coinciding with changes of Pb-isotopes in the Arctic Ocean. This latter change post-dates the intensification of NHG at 3.1 to 2.5 Ma and reflects an increase in the input of material eroded from the Archean Shield of Canada and Greenland. Shifts in Nd- and Pb-isotope compositions in a crust from the Blake Plateau occur before ∼5 Ma and most prominent at ∼8 Ma suggest that water masses from either the Pacific or Southern Ocean influenced the isotope composition of this crust. The relatively high ε Nd values around 8 Ma recorded by the Blake Plateau crust are explained by a contribution of eastward flowing Pacific water through the Panama Gateway into the Caribbean Sea. This high ε Nd signal decreased between 8 and 5 Ma suggesting that the supply of Pacific water into the Caribbean became restricted. This is earlier than the Caribbean seawater salinity increase at 4.2 Ma deduced from δ 18O data, and may indicate that there was only a surface water connection between the Caribbean and Pacific between ∼5 and 4.2 Ma. The closure of the Panama Gateway to intermediate and deep water exchange (>200 m depth) apparently occurred much earlier than the intensification of Northern Hemisphere Glaciation at 3.1–2.5 Ma, and cannot therefore have been a direct cause of this climatic change, but may, as recently argued, only have been a necessary precondition.

Surface water connection and the macrozoobenthos of two types of floodplains on the upper rhine

AbstractMacrozoobenthos (especially gastropods) abundance data have been used to ordinate sampling stations on two floodplains of the Upper Rhine with different hydraulic regimes: 30 species of gastropods were recorded in the area actively inundated by the Rhine, while backwaters that have not been flooded for over 50 years housed only 19 species.Potamopyrgus antipodarum is a characteristic species of the permanent aquatic biotopes fed by groundwater and connected with other floodplain waters. Small, isolated, and drying‐up former lateral channels and pools, slowly inundated during a flood, are characterized by Planorbis planorbis with Bathyomphalus contortus. Gyralus albus and Valvata cristata are characteristic of small, partly isolated, and partly drying‐up water bodies of the active floodplain, which are inundated rapidly and very turbulently during the flood. Due to restricted hydrological dynamics the waterbodies of the former floodplain were mainly inhabited by ubiquitous species.

Paleoclimatology and paleo-oceanography of the Norwegian and Greenland Seas: The last 450,000 years

Planktonic foraminiferal assemblages in Norwegian Sea sediments show that during the past 450,000 years a glacial regime, characterized by permanent sea-ice cover and the absence of the Norwegian Current, prevailed in the Norwegian Sea. These extremely cold conditions were interrupted by short, quasi-periodic (period of about 100,000 years) incursions of water warm enough to reduce sea-ice cover on a seasonal basis. Only the two most recent incursions were of sufficient intensity to bring relatively warm Norwegian Current waters into the region and thus justify here the name “interglacial”: the last interglacial (about 120,000 B.P.) and the Holocene. The absence of the Norwegian Current from the Norwegian Sea for all but about 20,000 of the last 450,000 years has had two important effects. First, a major source of heat for the Scandinavian land mass was not present except during the Holocene and the last interglacial. Thus, Scandinavia probably enjoyed a climate much like, or more severe than, that of Spitsbergen for most of the last 450,000 years. Large ice sheets were probably the rule rather than the exception. Second, the source of saline water for the formation of North Atlantic Deep Water was not present. This fact, together with the prevailing ice cover, prevented formation of a deep-water mass, except during the Holocene and the last interglacial. Deep water in the North Atlantic for all the remainder of the last 450,000 years must have formed elsewhere and by another mechanism. The prevailing ice-covered condition of the Norwegian Sea rules out the possibility of an open surface-water connection between the Arctic and North Atlantic oceans for all of the last 450,000 years. This is further evidence that the Ewing-Donn theory of an ice-free Arctic Ocean is incorrect. Of all the Pleistocene interglacial events recognized in temperate and low latitudes, only the last interglacial (Eemian) and the Holocene were intense enough to transport warm water into the Norwegian Sea and melt large amounts of sea ice. Future theories to explain climatic change must account for these anomalously warm interglacials as well as the extremely cold average conditions of the Norwegian Sea.