David J. Barclay

Tree-ring-dated 'Little Ice Age' histories of maritime glaciers from western Prince William Sound, Alaska

Tree-ring studies at 13 glacier forefields in western Prince William Sound show‘Little Ice Age’ glacial fluctuations were strongly synchronous on decadal timescales. Cross-dated glacially overrun trees at eight sites indicate ice margins advanced in the early (late twelfth through thirteenth centuries) and middle (seventeenth to early eighteenth centuries)‘Little Ice Age’. Tree-ring dates of 22 moraines at 13 glaciers show two main periods of stabilization. The earlier of these, in the first decades of the eighteenth century, overlaps with the second period of glaciers overrunning trees and marks culmination of this middle‘Little Ice Age’ expansion. Stabilization of moraines on nine of the study forefields in the latter part of the nineteenth century delineates a third interval of‘Little Ice Age’ glacial advance. The detailed‘Little Ice Age’ record from land-terminating glaciers in western Prince William Sound is consistent on a timescale of decades with four other tree-ring-dated glacial histories from across the northern Gulf of Alaska. This coastal northeastern Pacific glacial record reveals the structure of the‘Little Ice Age’ in the region and provides a strong basis for comparison with other proxy climate records spanning the past 1000 years.

Expansion of alpine glaciers in Pacific North America in the first millennium A.D

Radiocarbon ages and lichen-dated moraines from 17 glaciers in coastal and near- coastal British Columbia and Alaska document a widespread glacier advance during the first millennium A.D. Glaciers at several sites began advancing ca. A.D. 200-300 based on radiocarbon-dated overridden forests. The advance is centered on A.D. 400-700, when glaciers along an ;2000 km transect of the Pacific North American cordillera overrode forests, impounded lakes, and deposited moraines. The synchroneity of this glacier ad- vance and inferred cooling over a large area suggest a regional climate forcing and, to- gether with other proxy evidence for late Holocene environmental change during the Me- dieval Warm Period and Little Ice Age, provide support for millennial-scale climate variability in the North Pacific region.

A 1119-year tree-ring-width chronology from western Prince William Sound, southern Alaska

Living and subfossil trees from glacier forefields are used to develop a 1119-year-long tree-ringwidth chronology. Strong cross-dating among ring-width series from sites up to 60 km apart and an analysis of sample homogeneity support combination of all samples into a single, regional composite chronology. Comparison with instrumental climate data indicates May through July temperatures of the growth year are the primary control on ring-widths. Multidecadal-length warm periods in western Prince William Sound during the past 800 years were centred on AD 1300, 1440 and possibly 1820. Multidecadal-length cool periods were centred on AD 1400, 1660 and 1870. This is the first tree-ring chronology from the Gulf of Alaska region to extend into the first millennium AD.

Surface air temperature variability reconstructed with tree rings for the Gulf of Alaska over the past 1200 years

A 1200-year-long tree-ring width record from living and subfossil mountain hemlock wood is used to reconstruct February through August temperatures for the Gulf of Alaska, providing a record of past climate variability for the Northeast Pacific sector that captures interannual to centennial timescales. The moderate elevation at the tree-ring sites has allowed these trees to retain their temperature signal without evidence of the so-called divergence effect, or underestimation of tree-ring inferred temperature trends, which is observed at many northern latitude forest locations. This ‘divergence-free’ reconstruction reveals centennial trends that include a warm interval centered on ad 950 for coastal Alaska that occurs around the time of the ‘Medieval Warm Period’, a warming that is only rivaled by recent decades. Spectral analysis of this reconstruction supports the centennial pacing identified as a 170–220-year cadence consistent with solar variability. On the decadal to bidecadal scale, the reconstruction reveals ~10- and 18-year cycles, which have been observed elsewhere in climate records for western North America and are linked to solar and lunar tidal forcing, respectively. Temperature minima that occur at ad 969–970 and 1698–1700 correspond with the timing of major volcanic events. This tree-ring reconstruction supports centennial modes of solar forcing as a driver of surface air temperatures in the Gulf of Alaska, with lunar tidal, solar variability, internal variability, and volcanism, impacting climate on annual to decadal timescales.

Holocene history of Hubbard Glacier in Yakutat Bay and Russell Fiord, southern Alaska

Stratigraphic and geomorphic data defined by radiocarbon ages, tree-ring dates, and historical observations provide evidence of three major Holocene expansions of Hubbard Glacier. Early in each advance the Hubbard Glacier margin blocked Russell Fiord to create Russell lake, raising base level and causing stream beds and fan deltas throughout the Russell drainage basin to aggrade. Each Hubbard Glacier expansion continued with an ice lobe advancing through Disenchantment and Yakutat Bays in the west, and an eastern lobe advancing into Russell Fiord. The earlier two Holocene expansions were, respectively, under way at 7690 and 5600 calibrated yr B.P., and each advance culminated more than 1 k.y. later. The late Holocene advance was under way by 3100 yr ago and reached ∼13 km farther south in Russell Fiord than the preceding two expansions. Late Holocene deglaciation of Yakutat and Disenchantment Bays was complete before A.D. 1791; Nunatak Glacier flowing from neves east of Russell Fiord became the primary ice source to the Russell Fiord lobe at or before this date. Ice retreat from the southern end of Russell Fiord began in the late eighteenth century and the penultimate Russell lake drained ca. A.D. 1860. The relatively slow advances and more rapid retreats of Hubbard Glacier are consistent with the model of the iceberg-calving glacier cycle. Hubbard Glacier is currently advancing and will likely reestablish Russell lake in the near future, affecting local fisheries. However, glacier lobes are unlikely to reach the area of the town of Yakutat, built on late Holocene glacial deposits, in the next 1 k.y.

A Revised and Extended Holocene Glacial History of Icy Bay, Southern Alaska, U.S.A

Abstract Tidewater glaciers have coalesced to advance through Icy Bay, Alaska, three times during the past 3800 yr. Radiocarbon ages show that the first of these expansions was underway by 3750 cal yr B.P. and culminated at the outer coast between 3505 and 3245 cal yr B.P. Subsequent recession and readvance brought the ice margin back to the outer coast by 1525 cal yr B.P. (cal a.d. 425) where it remained for about 650 yr before retreating. Tree-ring cross-dates of glacially killed trees show that the most recent ice advance was underway through the inner bay by the a.d. 1640s and reached into the outer bay in the 1810s. Historical data support ice expansion through the outer bay in the early 19th century and show a late 19th century maximum prior to 20th century retreat. These results are a significant revision and extension of previous studies of the Holocene glacial history of Icy Bay. Average advance rates for the most recent expansion were typical of modern tidewater glaciers in the inner bay but much faster in the outer bay; shallow water here may have been important to this latter phase of unusually rapid advance.

A REVIEW OF LICHENOMETRIC DATING OF GLACIAL MORAINES IN ALASKA

Abstract. In Alaska, lichenometry continues to be an important technique for dating late Holocene moraines. Research completed during the 1970s through the early 1990s developed lichen dating curves for five regions in the Arctic and subarctic mountain ranges beyond altitudinal and latitudinal treelines. Although these dating curves are still in use across Alaska, little progress has been made in the past decade in updating or extending them or in developing new curves. Comparison of results from recent moraine‐dating studies based on these five lichen dating curves with tree‐ring based glacier histories from southern Alaska shows generally good agreement, albeit with greater scatter in the lichen‐based ages. Cosmogenic surface‐exposure dating of Holocene moraines has the potential to test some of the assumptions of the lichenometric technique and to facilitate the development of a new set of improved lichen dating curves for Alaska.

An 850 year record of climate and fluctuations of the iceberg-calving Nellie Juan Glacier, south central Alaska, U.S.A.

Abstract Tree-ring cross-dates of 46 glacially killed trees show that the tidewater Nellie Juan Glacier, Alaska, advanced seaward during the 16th and 17th centuries AD. Ice-scarred trees at the late-Holocene end moraine indicate that the terminus was at its recent maximum from 1842 to 1893. Historical observations and photographs show that subsequent slow retreat changed to rapid iceberg-calving retreat after 1935, and that the tidewater terminus had withdrawn about 3.3 km from the late-Holocene maximum by 1992. Comparison with paleoclimate records from nearby land-terminating glaciers and an 850 year tree-ring-width chronology indicates that the timing of the 19th-century maximum stand of Nellie Juan Glacier was controlled by changes in summer temperature and radiation. However, rapid iceberg-calving retreat did not begin until 40 years of slow retreat had brought the tidewater terminus back from the terminal moraine shoal. Therefore, both the dimensions of the terminal moraine shoal and the magnitude and duration of climate change were important in initiating rapid retreat of this tidewater glacier system.

Tree-Ring Dating of Historic Buildings in Willsboro, Northeastern New York, and Development of Regional Chronologies for Dendroarchaeology

Abstract Historical timbers have been sampled from buildings at 13 sites in Willsboro, New York, on the west shore of Lake Champlain. Ring-width series from 139 timbers have been successfully crossdated and used to develop tree-ring chronologies for ash (Fraxinus spp.), oak (Quercus spp.), pine (Pinus spp.), eastern hemlock (Tsuga canadensis (L.) Carr.), and spruce (Picea spp.), which collectively span A.D. 1555 to 1878. Tree cutting dates suggest that Windyview Manor was likely built in or soon after 1799, and a barn and farmhouse at the 1812 Homestead were built in or soon after 1812 and 1813, respectively. These dates are all consistent with documentary records for these sites. Aggregate data for the town suggest a shift in wood use for building during the 19th Century, with ash and oak commonly used for large frame timbers from the 1790s to 1820s, and hemlock and spruce dominating from the 1830s to 1860s. Chronologies developed in this project are among the first from historical timbers for northern New York and will facilitate further dendroarchaeological work in the region.

PREFACE TREE-RING STUDIES IN NEW YORK STATE: PAST AND PRESENT (A TREE-RING RESEARCH SPECIAL ISSUE)

Abstract New York State (NYS) has a long and significant history of tree-ring research. Some of the earliest dendroarchaeological and dendroclimatic work in eastern North America was done in NYS, and 1970s studies in Hudson Valley in the east of the state were important for demonstrating that drought records could be reconstructed from trees growing in humid environments. Some recent work in NYS is described in this issue of Tree-Ring Research, including tree-ring dating and provenancing of a boat in New York City, dendroarchaeological studies in a town in northeastern NYS, dendrogeomorphological work in central NYS, and a dendroclimatic investigation of two range-margin Juniperus species growing on alvars. The last of the five NYS papers in this issue provides a personal historical perspective on the beginnings of drought reconstructions in the Hudson Valley. There is considerable potential for future work in New York with extension of existing studies and work in new areas and with new tree species.