ColumbiaQ by Pellatt et al., 2002. Palaeogeography, Palaeoclimatology,

Palaeoecology 203, 337–342.

Easterbrook, D.J., Kovanen, D.J., 1998. dPre-younger Dryas resurgence of

the southwestern margin of the Cordilleran Ice Sheet, British Columbia,

CanadaT: comments: Boreas 27, 225–230.

Heier-Nielsen, S., Heinemeier, J., Nielsen, H.L., Rud, N., 1995. Recent reservoir

ages for Danish fjords and marine waters. Radiocarbon 37, 875–882.

Hutchinson, I., James, T.S., Reimer, P.J., Bornhold, B.D., Clague, J.J.,

2004. Marine and limnic radiocarbon reservoir corrections for studies of

late- and postglacial environments in Georgia Basin and Puget

Lowland, British Columbia, Canada and Washington, USA. Quaternary

Research 61, 193–203.

Kovanen, D.J., 2002. Morphologic and stratigraphic evidence for Allerbdand Younger Dryas age glacier fluctuations of the Cordilleran Ice Sheet,

British Columbia, Canada and Northwestern Washington, U.S.A.

Boreas 31, 163–184.

Kovanen, D.J., Easterbrook, D.J., 2002a. Paleodeviations of radiocarbon

marine reservoir values for the NE Pacific. Geology 30, 243–246.

Kovanen, D.J., Easterbrook, D.J., 2002b. Timing and extent of Allerod and

Younger Dryas age (ca. 12,500–10,000 14C yr B.P.) oscillation of the

Cordilleran Ice Sheet in the Fraser Lowland, western North America.

Quaternary Research 57, 208–224.

Pellatt, M.G., Mathewes, R.W., Clague, J.J., 2004. Reply to comments on

bImplication of a late-glacial pollen record for the glacial and climatic

history of the Fraser Lowland, British ColumbiaQ by Easterbrook, 2004.

Palaeogeography, Palaeoclimatology, Palaeoecology 203, 343–346.

Rodrigues, C., 1988. Late Quaternary invertebrate faunal associations and

chronology of the western Champlain Sea. In: Gadd, N.R. (Ed.), The

Late Quaternary Development of the Champlain Sea Basin, Special

Paper 35, pp. 155–176. Geological Association of Canada, Ottawa.

Southon, J.R., Nelson, D.E., Vogel, J.S., 1990. A record of past ocean–

atmosphere radiocarbon differences from the northeast Pacific. Paleo-

ceanography 5, 197–206.

Stuiver,M., Braziunas, T.F., 1993.Modelling atmospheric 14C influences and14C ages of marine samples to 10,000 BC. Radiocarbon 35, 137–189.

Don J. Easterbrook

Department of Geology, Western Washington University,

Bellingham, Washington, DC 98225, USA

Earth and Space Sciences, University of Washington,

Seattle, Washington, DC 98195, USA

E-mail address: dbunny@cc.wwu.edu.

Corresponding address. Department of Geology,

Western Washington University, Bellingham,

Washington, DC 98225, USA.

Fax: +1 360 6507302.

17 September 2004

Reply to letter to the editor from Easterbrook and

Kovanen re Quaternary Research 61, 193–203.

We wish to apologize to Easterbrook, Kovanen, and

others for not including their names as sources of informa-

tion in the supplementary table supplied with Hutchinson et

al. (2004); an early version of the table was inadvertently

transmitted rather than the final document. Despite vigilance,

mistakes do occasionally occur. A corrected final version of

our supplementary table is provided here.

On matters of substance, however, we respectfully

disagree with most of Easterbrook and Kovanen’s criticisms.

They castigate us for omitting discussion on the sites from

which they derive the reservoir values cited in Kovanen and

Easterbrook (2002). Our reluctance to discuss these sites

stemmed in part from the fact that the interpretation of the

stratigraphic sequence at one site (Bradner Pit) has been the

subject of debate between them and some of the authors of

this paper for several years. We felt that little purpose would

be served in reopening this debate on the late-glacial history

of the Fraser Lowland in a paper focusing on reservoir

corrections. Our other reason was that no stratigraphic

information has been published by Easterbrook and Kovanen

on the Axton Pit site, and it is consequently impossible to

determine the provenance of the shell-wood pairs they report

from this site or to assess their assertion that the inferred

glaciomarine deposits represent the same unit. Clearly our

desire to avoid controversy has had the opposite effect.

Their primary evidence in support of the claim that these

inferred glaciomarine deposits form a single unit is that the

wood fragments and pine cone that they sampled from the

Bradner and Axton pits yield uniform ages [overall mean =

11,740 F 60 14C yr B.P.; T’ = 1.35; X 2 (0.05) = 11.10].

Terrestrial detritus, however, merely furnishes an upper

bound on the age of neritic and shoreface sediments;

contemporaneity of deposition at Bradner and Axton pits

can only be demonstrated from ages on autochthonous

material. In this case, the marine shell samples in the inferred

glaciomarine deposits come from statistically independent

populations [Bradner weighted mean: 12,960 F 20 14C yr

B.P.; Axton weighted mean: 12,720 F 20 14C yr B.P.; T’ =

54.68; X 2 (0.05) = 11.10]. Kovanen and Easterbrook (2002)

note this discrepancy, but disregard it and combine the

samples to develop a regional marine reservoir correction for

the late-glacial period. The greater age of the shells at

Bradner Pit compared to Axton Pit implies either, as Clague

et al. (1997) argued, that shells at Bradner Pit are reworked

from older glaciomarine sources, or, as Hutchinson et al.

(2004) proposed, that late-glacial marine reservoir values in

enclosed waters may display local variation.

This latter proposal was prompted in part as a reaction to

the conclusion by Kovanen and Easterbrook (2002) that the

enhanced late-glacial marine reservoir value (compared to

the modern) that they report from two sites in a lowland on

the inner shore of an enclosed sea is a consequence of

changes in circulation patterns in the northeast Pacific

Ocean or to global changes in ocean ventilation. Their

conclusions would have been stronger if they had provided

data spanning a larger region. Instead, the greater age of the

shells at the Bradner Pit in the Fraser Lowland compared to

other late-glacial sites in southern Georgia Basin may be a

result of a local enhancement of the marine reservoir effect

at this relatively sheltered location. Mollusks growing in

shallow water environments in locations in valley or fjord

head sites may be exposed to waters with a greater apparent

age, either from the thawing of 14C-depleted ice from

doi:10.1016/j.yqres.2004.10.004

Letters to Editor226

adjacent tidewater glaciers or from the incorporation of old

carbon leached from newly emergent glacial deposits. Both

of these factors may have played a role in modifying the

apparent age of marine waters in the Georgia Basin and

Puget Lowland as the Cordilleran ice sheet rapidly waned

after 14,000 14C yr B.P.

Easterbrook and Kovanen argue against substantial melt-

water contributions in the Fraser Lowland based on y18Ovalues of �0.1x, �0.5x, and �0.8x from late-glacial

marine shells. These values would indicate limited meltwater

discharge into a polar fjord head environment, but the ice of

low-elevation glaciers in more temperate maritime areas may

be only slightly fractionated compared to waters of the source

region. For example, ice from Aialik Glacier on the Kenai

Peninsula of Southern Alaska has a y18O value of �2.9x,

only slightly more negative than the offshore surface waters

of the Gulf of Alaska (y18O = �1.5x to �2.4x) (Kipphut,

1990). The oxygen isotope ratio in the shell of a mollusk

growing below the surface mixed layer close to the tidewater

margin of a temperate glacier is therefore likely to be a poor

guide to meltwater volume. A further difficulty arises from

the fact that surface waters of the Strait of Georgia were likely

frozen for much of the year in late-glacial time (Guilbault et

al., 2003), and the presence of sea ice bseriously complicates

the interpretation of variations in the (oxygen) isotopic

composition of surface watersQ (Rohling, 2000, pp. 9–10).Hutchinson et al. (2004) show that the incorporation of

old carbon into the basal gyttja of lakes in the Georgia Basin

and Puget Lowland in early deglacial time yields radiocarbon

ages from bulk samples that are initially about 600 yr too old.

Deposition of terrigenous organic and inorganic carbon into

the local marine environment may have a similar effect.

McKay et al. (2004) note that bthe terrigenous fraction

accounts for 50–70% of the total organic matter pool [on the

continental slope to the west of Vancouver Island] during the

late glacial and early deglacial (prior to 13,500 cal yr B.P.), is

approximately half this proportion (between 13,400 and

11,200 cal yr B.P.), and then progressively decreases to only

few percent in the latter part of the HoloceneQ (p. 269). Bulksamples of this organic matter yielded radiocarbon ages that

were up to 12,300 14C yr older than those from contempora-

neous planktonic foraminifers (McKay et al., 2004). The

remobilization of a small part of the old carbon in this sink

and its uptake from pore and bottom waters by mollusks

living in shallow coastal environments would be sufficient to

account for the enhanced marine reservoir effect in late-

glacial time.

Easterbrook and Kovanen state: bthe authors cite an

assumed reservoir value of �820 yr (the correct citation is

�800 yr, not �820) dfrom wood and shell samples in a

glaciomarine unit at a critical site,T which is based on

Southon et al.’s (1990) data from the Queen Charlotte

Islands. However, as noted by Hutchinson et al. (2004), the

calibration site is actually a high-energy beach deposit, not

glaciomarine drift.Q We suggest they reread our original

statement, in which it is clear that bfrom wood and shell

samples in a glaciomarine unit at a critical siteQ refers to

Clague et al. (1997), not Southon et al. (1990).

Finally, we concur with Easterbrook and Kovanen that

many more AMS radiocarbon ages on marine organisms

from this period are needed in this region. But alternative

hypotheses for enhanced marine reservoir effects should be

rigorously scrutinized before primacy is given to explan-

ations linked to global climatic and oceanographic change.

References

Clague, J.J., Mathewes, R.W., Guilbault, J.-P., Hutchinson, I., Ricketts, B.D.,

1997. Pre-Younger Dryas resurgence of the southwestern margin of the

Cordilleran ice sheet, British Columbia, Canada. Boreas 26, 261–277.

Guilbault, J.-P., Barrie, J.V., Conway, K., Lapointe, M., Radi, T., 2003.

Paleoenvironments of the Strait of Georgia, British Columbia during the

last deglaciation: microfaunal and microfloral evidence. Quaternary

Science Reviews 22, 839–857.

Hutchinson, I., James, T.S., Reimer, P.J., Bornhold, B.D., Clague, J.J.,

2004. Marine and limnic radiocarbon reservoir corrections for studies of

late- and postglacial environments in Georgia Basin and Puget

Lowland, British Columbia, Canada and Washington, USA. Quaternary

Research 61, 193–203.

Kipphut, G.W., 1990. Glacial meltwater input to the Alaska Coastal

Current: evidence from oxygen isotope measurements. Journal of

Geophysical Research 95, 5177–5181.

Kovanen, D.J., Easterbrook, D.J., 2002. Paleodeviations of radiocarbon

marine reservoir values for the northeast Pacific. Geology 30, 243–246.

McKay, J.L., Pedersen, T.F., Kienast, S.S., 2004. Organic carbon

accumulation over the last 16 kyr off Vancouver Island, Canada:

evidence for increased marine productivity during the deglacial.

Quaternary Science Reviews 23, 261–281.

Rohling, E.J., 2000. Paleosalinity: confidence limits and future applica-

tions. Marine Geology 163, 1–11.

Southon, J.R., Nelson, D.E., Vogel, J.S., 1990. A record of past ocean-

atmosphere radiocarbon differences from the northeast Pacific. Paleo-

ceanography 5, 197–206.

Ian Hutchinson

Department of Geography, Simon Fraser University,

Burnaby, BC, Canada V5A 1S6

E-mail address: ianh@sfu.ca.

Corresponding author. Fax: +1 604 291 5841.

Thomas S. James

Geological Survey of Canada, Sidney,

B.C., Canada V8L 4B2

Paula J. Reimer

School of Archaeology and Palaeoecology,

Queen’s University Belfast, Belfast, BT7 1NN, U.K.

Brian D. Bornhold

Centre for Earth and Ocean Sciences, University of

Victoria, Victoria, B.C., Canada V8W 2Y2

John J. Clague

Department of Earth Sciences, Simon Fraser University,

Burnaby, B.C., Canada V5A 1S6

12 October 2004

doi:10.1016/j.yqres.2004.10.003

Letters to Editor 227