Marlow G. Pellatt

High-resolution Holocene vegetation history and climate from Hole 1034B, ODP leg 169S, Saanich Inlet, Canada

Abstract High-resolution pollen analysis of laminated marine sediments from ODP Hole 1034B in Saanich Inlet, British Columbia reveals changes in vegetation and inferred climate during the Holocene. Four main pollen zones are discerned using constrained cluster analysis. Although the timing of major vegetation changes at the Saanich Inlet is similar to other study sites in the Pacific Northwest, the composition of pollen assemblage zones is different from the mainland sites. Vegetation assemblages reconstructed from the pollen and spore record include a Douglas-fir (Pseudotsuga menziesii) parkland with abundant grass (Poaceae) and bracken (Pteridium) between 11,450 and 8300 BP (all ages are calibrated calendar years), oak (Quercus) savanna or parkland with high grass and bracken (8300–7040 BP), a mixed deciduous/coniferous forest with oak, western hemlock (Tsuga heterophylla) and Douglas-fir (7040–5750 BP), and the development of modern coastal temperate forest with the marked expansion of cedar (Cupressaceae), western hemlock, spruce (Picea) and Douglas-fir (5750–1050 BP). Climatic periods inferred from the cores include an early Holocene warm/dry interval (11,450–8300 BP), a warm period with mild winters (8300–7040 BP), a period of transitional mid-Holocene climate (7040–5750 BP), and the advent of a relatively cool/wet neoglacial climate after 5750 BP. Modern conifer forests and oak savannas became established by about 3800 BP. The Saanich Inlet pollen record indicates that vegetation and inferred climate change was particularly rapid between 8700 and 8300 BP when grass and bracken abruptly decrease and oak becomes a significant component of the paleovegetation. Because neoglacial conditions have prevailed from 3800 years to present in the Pacific Northwest, factors other than climate, such as anthropogenic modification of the landscape, may be responsible for the persistence of oak savannas.

Holocene treeline and climate change in the subalpine zone near Stoyoma Mountain, Cascade Mountains, southwestern British Columbia, Canada.

Multiproxy paleoecological investigation of a small lake in the high subalpine zone near Stoyoma Mountain, northern Cascade Mountains of British Columbia, reveals significant change in vegetation, limnic conditions, and inferred climate throughout the Holocene (last 10,000 radiocarbon years). Three zones of distinct pollen, plant macrofossil, and chironomid assemblages are apparent in the sediment core from 3M Pond (informal name). A dry, sparsely vegetated spruce parkland and a warm-adapted chironomid community existed in and around the study sites in the early Holocene (ca. 10,000 to 7000 14C yr BP). Between 7000 and 3500 14C yr BP, Engelmann spruce–subalpine fir forest conditions established and then declined around 3M Pond leading to modern subalpine parkland conditions from 3500 14C yr BP to present. Chironomid communities at 3M Pond between 7000 and 3500 14C yr BP are indicative of warmer waters than present, but show a transition to modern assemblages. Three climatic regimes are identified near Stoyoma Mountain: (1) the early Holocene xerothermic period (10,000 to 7000 14C yr BP, (2) a period of climatic transition in the mid-Holocene (7000 to 3500 14C yr BP), and (3) cool, modern neoglacial conditions (after 3500 14C yr BP). These findings confirm vegetation and inferred climate changes identified at Cabin Lake, British Columbia (a nearby lake in the subalpine forest). Changes in treeline position, plant communities, chironomid communities, and inferred climate are nearly synchronous and validate the multiproxy approach for paleoecological reconstruction. Chironomid-based paleotemperature reconstructions confirm earlier evidence that the early Holocene was significantly warmer than present, with estimated summer water surface temperatures up to 4°C higher than today.

Climate Change in Coastal British Columbia — A Paleoenvironmental Perspective

A comprehensive review of paleoenvironmental data provides the basis for evaluating natural climate variability in southwestern British Columbia. Key indicators of past changes include paleolimnological, paleobotanical, glaciological and dendroclimatological evidence. Lacustrine sediments record the rapid transition from a glacial to an interglacial climate 12,500 to 9000 14C yr BP. Peak summer temperatures (about 3 °C warmer than present) and minimum precipitation were recorded ca. 9000 to 7000 14C yr BP, but were likely accompanied by winter temperatures colder than today. Mid-Holocene cooling appears to have occurred sooner on the coast of British Columbia (~ 5000 14C yr BP) than in the southern interior where summer temperatures gradually declined ca. 7000 to 3000 14C yr BP, as wetter conditions and a stronger Aleutian low developed. Many glacial advances have been recorded in the past 3500 years, with most glacial maxima dating to the mid 19th century. A general glacial retreat has accompanied recent warming.

Postglacial changes in chironomid communities and inferred climate near treeline at Mount Stoyoma, Cascade Mountains, southwestern British Columbia, Canada

Analysis of the distributions of chironomid (midge) and other dipteran subfossils from two high elevation lake sediment cores in the Cascade Mountains reveals changes in midge communities and inferred climate since the late-glacial. Cabin Lake and 3M Pond are located near treeline in the subalpine Engelmann Spruce/Subalpine Fir biogeoclimatic zone of British Columbia. In Cabin Lake, chironomid head capsule assemblages depict a typical late-glacial community, and three distinct Holocene communities. In Cabin Lake, the late-glacial community is composed of cold-stenothermous taxa dominated by Stictochironomus, Mesocricotopus, Heterotrissocladius, Parakiefferiella nigra, Protanypus and Paracladius, whereas warm water midges are absent or rare, indicating cold conditions. A late-glacial chironomid community was not found in 3M Pond. In both lakes the early Holocene is dominated by a diverse warm-adapted assemblage, corresponding to the warm climatic conditions of the xerothermic period. Cabin Lakes mid-Holocene zone records a decrease in relative abundance of the warm water types and is accompanied by an increase in cold-stenotherms. At 3M Pond this period shows a dramatic loss in diversity of warm-adapted taxa, as the temperate genus Dicrotendipes dominates. This zone corresponds to Hebdas (1995) mesothermic period. Further cooling in the late Holocene (to modern conditions) is inferred from continued reduction of warm water midges and persistence (at Cabin Lake) or appearance (at 3M Pond) of a cold-stenothermal community. This late Holocene cooling is similar in timing to Neoglacial advances in the Coast, Cascade, and Rocky Mountains of southern British Columbia. Similarities in the timing of chironomid and vegetation community changes at these high elevation sites, along with the more rapid response time of the Chironomidae, support the sensitivity of midges to postglacial climatic change at high elevation sites.

Paleoecology of postglacial tree line fluctuations on the Queen Charlotte Islands, Canada

AbstractPlant macrofossil and pollen analyses of sediments from a high elevation lake on the Queen Charlotte Islands, British Columbia, reveal changes in vegetation and inferred climate during the Holocene. Pollen and macrofossil zones at Louise Pond correlate well during the early Holocene, showing that vegetation changes recorded in the fossil diagrams occurred near the lake basins. Paleobotanical evidence for local presence of western hemlock (Tsuga heterophylla [Raf.] Sarg. trees between ca 9 600 and 8 700 ± 150 yr BP indicates a warmer climate than today in the early Holocene. Declining western hemlock and increasing mountain hemlock (Tsuga mertensiana Bong.) fossils suggest some lowering of tree line at Louise Pond between about 8 700 ± 150 and ca 7 300 yr BP. Radiocarbon dates from Shangri-La Bog and SC-1 Pond (7 190 ± 100 yr BP and 7 180 ± 110 yr BP respectively) show that climatic deterioration was occurring regionally by this time on the Queen Charlotte Islands. The development of upper subalpin...

Implications of a late-glacial pollen record for the glacial and climatic history of the Fraser Lowland, British Columbia

Abstract Late-glacial sediments at Mike Lake in the Fraser Lowland of southwestern British Columbia shed light on the timing and significance of the Younger Dryas and Sumas events on the west coast of Canada. Five pollen zones span the period from about 11 700 to 9700 radiocarbon years before present (yr BP) or 13 700 to 11 200 calibrated calendar years before present (cal BP). Climate during this interval is inferred to have ranged from cool continental to warm and dry. Changes in pollen assemblages, lithology, and loss on ignition in Mike Lake sediments deposited prior to 11 000 yr BP (13 000 cal BP) may signal the Sumas glacial advance, which has been dated elsewhere in the Fraser Lowland to this time. Palynologic and sedimentological data indicate that there was much climatic and ecological variability in southwestern British Columbia during the Younger Dryas chronozone. Detrended correspondence analysis of modern pollen from lake-sediment surface samples collected throughout British Columbia is used to compare Mike Lake fossil pollen assemblages to modern vegetation zones. The inferred vegetation assemblage during most of the Younger Dryas chronozone indicates a progressively warming climate with a cool interval between 10 400 and 10 000 yr BP. The pollen assemblage in this interval is similar to that of present subalpine forests on the west coast of Canada. The cooling coincides with the later part of the Younger Dryas chronozone and occurred too late to be the driving mechanism for the final Sumas advance, which peaked around 11 300 14C yr BP (13 200 cal BP).

The Water Chemistry of Shallow Ponds around Wapusk National Park of Canada, Hudson Bay Lowlands

Understanding the structure and function of ecosystems in Canadas national parks is essential in fulfilling the Parks Canada Agencys mandate to manage for ecological integrity. Wapusk National Park is representative of the Hudson Bay Lowlands and small lakes and ponds make up a considerable component of the landscape. The Hudson Bay Lowlands have experienced relatively recent isostatic rebound from submarine conditions, hence proximity to the coast was found to be a major factor in determining the concentration of dissolved salts in pond water. It was observed that the ionic composition of the water in ponds throughout much of the park is consistent, indicating that most of the ponds are an expression of surface water maintaining little connection to groundwater. The prevalence of permafrost throughout much of the park is likely the reason for this stability. Ponds within the park also show considerable variability in the amount of dissolved organic carbon (DOC) they contain. DOC shows a strong north-south and east-west trend. Ponds in the northeast of the park have lower DOC values while ponds in the southwest of the park have higher levels of DOC. Changes in DOC within the park appear to be driven by changes in the terrestrial vegetation surrounding the ponds. Climatically mediated changes in northern tree line and permafrost are likely to cause the greatest alteration of aquatic habitats in Wapusk National Park. The paucity of background data makes it impossible to assess the amount of change that may have already occurred in the park. This research provides the first landscape-level study for the area and shows that there are distinct limnological patterns over this landscape that are likely to be sensitive to climate change and should be readily detectable with ongoing monitoring.

Changes to the Productivity and Trophic Structure of a Sockeye Salmon Rearing Lake in British Columbia

Abstract In the 1990s, the returns of sockeye salmon Oncorhynchus nerka to Long Lake in Smith Inlet, British Columbia, declined substantially. In 1997 the commercial fishery was closed, and it will not be reopened until the population shows signs of sustained recovery. We examined paleolimnological and geochemical variables from a sediment core extracted from Long Lake in 2002. The nitrogen isotope concentration (δ15N), which is associated with salmon production, declined to unprecedented levels in the 20th century. Sodium and other alkali elements have also decreased at a generally accelerating pace since the mid-19th century, and there are indications that the headwater glacier has receded apace. Accompanying these trends were notable changes in proxies for lake ecology, including the size and abundance of planktonic invertebrates. The timing and behavior of these unprecedented changes in the sedimentary record point to potential impacts from both commercial fishing and climate change.

A midge-salinity transfer function for inferring sea level change and landscape evolution in the Hudson Bay Lowlands, Manitoba, Canada

We compared water chemistry and environmental data with midge assemblage data, using multivariate analysis to assess the environmental gradients that limit midge (Chironomidae, Chaoboridae and Ceratopogonidae) distributions in the Hudson Bay Lowlands, northeastern Manitoba, Canada. Midge remains, comprising 62 taxa, were obtained from surficial sediments of 63 ponds. Ponds were sampled to maximize the salinity gradient. Specific conductance ranged from 46 to 29,000 μS cm−1. Proximity to the coast was a principal determinant of pond salinity, with ponds closer to Hudson Bay shoreline more saline that those farther away. Multivariate analysis indicated that midge distributions have a significant relationship (