The 8.2 ka event was the last deglacial abrupt climate event. A reduction in the Atlantic meridional overturning circulation (AMOC) attributed to the drainage of glacial Lake Agassiz may have caused the event, but the freshwater signature of Lake Agassiz discharge has yet to be identified in δ18O of foraminiferal calcite records from the Labrador Sea, calling into question the connection between freshwater discharge to the North Atlantic and AMOC strength. Using Mg/Ca-paleothermometry, we demonstrate that ∼3°C of near-surface ocean cooling masked an ∼1.0‰ decrease in western Labrador Seaδ18O of seawater concurrent with Lake Agassiz drainage. Comparison with North Atlantic δ18O of seawater records shows that the freshwater discharge was transported to regions of deep-water formation where it could perturb AMOC and force the 8.2 ka event.
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 Sediment and faunal records from James and Hudson Bays, Hudson Strait, and the Labrador Sea support the drainage of Lake Agassiz around 8.2 ka [Andrews et al., 1995, 1999; Kerwin, 1996; Barber et al., 1999; Hillaire-Marcel et al., 2007; Lajeunesse and St-Onge, 2008; Roy et al., 2011; Lewis et al., 2012], and Hudson Strait geochemical records document the routing of Lake Agassiz drainage basin runoff during the 8.2 event [Carlson et al., 2009]. However, no direct evidence of a freshwater signal has been found in Labrador Sea δ18O of foraminiferal calcite (δ18Oc) coeval with the drainage of Lake Agassiz [Keigwin et al., 2005; Hillaire-Marcel et al., 2007, 2008]. One explanation for the lack of a δ18Oc signal is that the lake drainage was too short lived to be recorded by planktonic foraminifera [Andrews et al., 1999; Hillaire-Marcel et al., 2007], although a longer δ18Oc decrease should be evident from the breakup of the Laurentide Ice Sheet over Hudson Bay [Andrews et al., 1995, 1999] and the addition of the Lake Agassiz drainage basin to Hudson Bay [Clark et al., 2001; Hillaire-Marcel et al., 2007; Carlson et al., 2009]. Another explanation is that the discharged freshwater may have had little impact on Labrador Sea δ18Oc because Lakes Agassiz and Ojibway δ18O of approximately −25‰ was only marginally more negative than present-day runoff to James and Hudson Bays of −20‰ [Hillaire-Marcel et al., 2008]. However, even without a change in runoff δ18O, an increase in freshwater discharge as expected during Lake Agassiz drainage would still cause a decrease in Labrador Sea δ18O of seawater (δ18Osw) due to the increased volume of 18O-depleted freshwater [Barber et al., 1999; LeGrande et al., 2006]. Attributing the cause of the reduction in AMOC during the 8.2 ka event to the drainage of Lake Agassiz has also proven difficult, because Lake Agassiz discharge may have been mostly trapped against the Labrador shelf in a buoyant surface flow of the Labrador Current and not transported to regions of deep convection in the open ocean [Wunsch, 2010; Condron and Winsor, 2011]. These outstanding issues ultimately imply that freshwater discharge may not have caused the 8.2 ka event, raising the possibility that alternative mechanisms, like reduced solar activity, forced this and other abrupt climate events [Alley and Ágústdóttir, 2005; Rohling and Pälike, 2005]. Because δ18Oc is sensitive to changes in surface temperatures and local δ18Osw [e.g., LeGrande et al., 2006], we hypothesize that the magnitude of near-surface cooling during the 8.2 ka event masked aδ18Osw decrease in Labrador Sea δ18Oc from the drainage of Lake Agassiz.
 We test our hypothesis with core HU87033-017 from the Cartwright Saddle (54.62°N, 56.18°W, 514 m water depth) (Figure 1 and auxiliary material, Text S1, section S1), which is located in the pathway Lake Agassiz discharge would have taken upon exiting Hudson Strait [Condron and Winsor, 2011]. We investigate early Holocene sediment discharge from the Laurentide Ice Sheet with changes in weight percent coarse fraction (>63 μm). We document western Labrador Sea calcification temperatures (CT) of Neogloboquadrina pachyderma(sinistral) with flow-through Mg/Ca-paleothermometry (Text S1, section S4) [Klinkhammer et al., 2004]. N. pachyderma (s) is a pycnocline dwelling subpolar to polar planktonic foraminifer (Figure S1 and Text S1, sections S2 and S7). Combining our Mg/Ca CT record with the existing δ18Oc record of Andrews et al. from HU87033-017, we calculateδ18Osw (Text S1, sections S4–S8). Due to the low abundance of planktonic foraminifera tests, the core chronology is based on eight benthic, reservoir-corrected (450 years), calibrated14C dates of Andrews et al.  (Table S1 and Text S1, section S3).
 The N. pachyderma (s) CT record shows ∼2°C of warming ∼11.5–11.2 ka, with a more gradual trend to a CT maximum of ∼8°C at ∼9.7 ka (Figure 2c). CT subsequently cooled to 5–6°C between ∼9.5 and 8.3 ka, reaching a minimum of ∼3°C at ∼8.3 ka. At ∼8.0 ka, CT warmed to ∼4°C and reached ∼5°C by ∼7.5 ka, which is equivalent to late Holocene CT (Figure S1 and Text S1, section S7). Our δ18Osw record shows several deviations from the N. pachyderma (s) δ18Oc record of Andrews et al.  (Figures 2d and 2e). Between ∼11.2 and 9.7 ka, δ18Oc increased by ∼0.4‰, whereas δ18Osw increased by ∼1.2‰; thereafter, both records decreased by ∼1.0‰. At the same core depth as the ∼3°C of CT cooling but just preceding the increase in weight percent sand, δ18Osw further decreased by ∼1.0‰. δ18Osw then increased by ∼0.9‰ after ∼8.0 ka, and by another ∼0.4‰ by ∼7.0 ka.
4. Discussion and Conclusions
 The gradual increase in δ18Osw ∼11.5–9.7 ka may document the stabilization of the Laurentide Ice Sheet margin as it retreated onto the Labrador coast [Andrews et al., 1995, 1999]. The subsequent decrease after ∼9.7 ka (Figure 2b) likely reflects increased iceberg calving and meltwater plume deposition of sediment from renewed Laurentide retreat and the beginning of ice break-up in Hudson Strait after the Noble Inlet readvance, which is supported by the increase in weight percent sand (Figure 2b) from sediment in meltwater plumes and icebergs [Andrews et al., 1995, 1999; Jennings et al., 1998].
 The ∼1.0‰ further decrease in δ18Osw ∼8.3–8.0 ka identifies increased freshwater discharge into the Labrador Sea coincident with the drainage of Lake Agassiz. This depletion event was obscured in the δ18Oc record by the contemporaneous CT cooling of ∼3°C in the Labrador Sea that reflects the impact of cold Lake Agassiz runoff and regional cooling during the 8.2 ka event. The masking of this δ18Oc depletion by CT cooling is supported by climate model simulations of the break down in the relationship between temperature and δ18O of foraminiferal calcite during the 8.2 ka event [LeGrande et al., 2006], which is also observed at different subsurface depths in the North Atlantic with the application of Mg/Ca paleothermometry [Came et al., 2007; Thornalley et al., 2009]. Earlier studies of the Labrador Sea did not account for the effect of ocean cooling on δ18Oc during the 8.2 ka event, explaining why a δ18Oc decrease from the drainage of Lake Agassiz was previously suggested to be lacking [Keigwin et al., 2005; Hillaire-Marcel et al., 2007, 2008].
 We compare our δ18Osw decrease with other records of freshwater discharge during the 8.2 ka event to trace the path of freshwater from Hudson Bay. After flowing through Hudson Strait, we document the drainage of Lake Agassiz in the western Labrador Sea with the ∼1.0‰ δ18Osw decrease. In the northwest Atlantic at 43–37°N, δ18Oc records show depletions of 0.4–0.6‰, reflecting warming and/or increased freshwater discharge [Keigwin et al., 2005]. However, δ18Osw increases by ∼0.2‰ at 35°N in the northwest Atlantic (Figure 1) [Cléroux et al., 2012]. In contrast, δ18Osw decreases in the northeast Atlantic of ∼0.8‰ at ∼27°W to ∼0.4‰ at ∼18°W from foraminifera living at different subsurface water depths (Figures 1 and 3) [Ellison et al., 2006; Came et al., 2007; Thornalley et al., 2009]. These records thus document the dispersal of Lake Agassiz freshwater across the North Atlantic, with freshwater transported southwards as far as ∼37°N in the northwest Atlantic, and eastward into the northeast Atlantic. The decrease in δ18Osw anomalies to the south and east of the Labrador Sea likely shows the dilution of the freshwater signal along these transport paths (Figure 1).
 Conversely, the UVic high-resolution (0.2° × 0.4°) ocean model that includes a simplified atmosphere found that freshwater on the Labrador shelf could affect the AMOC within years of its discharge [Spence et al., 2008]. In addition, the UVic model simulated that the duration and maximum amplitude of the freshwater forcing and AMOC response are relatively insensitive to increasing resolution from low-resolution general circulation models (GCM) to high, eddy-resolving resolution [Spence et al., 2008]. We also find agreement between changes in δ18Oswby the NASA Goddard Institute for Space Studies fully-coupled GCM ModelE-R that includes water isotopes throughout the hydrologic cycle [LeGrande and Schmidt, 2008] and the observed decrease in δ18Osw records during the 8.2 ka event (Figure 1), similar to other coupled climate model studies [Meissner and Clark, 2006; Spence et al., 2008; Clarke et al., 2009]. These model-δ18Osw comparisons suggest that although Lake Agassiz runoff may have been initially trapped in boundary currents along eastern North America [Keigwin et al., 2005; Wunsch, 2010; Condron and Winsor, 2011], the freshwater eventually escaped from the continental shelf, was entrained in the Gulf Stream and North Atlantic Current, and reached regions of deep-water formation in the northeast Atlantic where it could affect the AMOC [Ellison et al., 2006; Kleiven et al., 2008; Hoogakker et al., 2011].
 A. Ungerer and S. Marcott assisted with Mg/Ca analyses. A. Mix discussed methodological approaches. Comments by three reviewers improved this manuscript. An Augustana College Student Summer Research Fellowship (J.S.H.), and the University of Wisconsin-Madison and National Science Foundation Paleoclimate Program (A.E.C.) funded this study. Samples were provided by the Bedford Institute of Oceanography.
 The Editor thanks two anonymous reviewers for their assistance in evaluating this paper.