Donald C. Barber

Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes

The sensitivity of oceanic thermohaline circulation to freshwater perturbations is a critical issue for understanding abrupt climate change. Abrupt climate fluctuations that occurred during both Holocene and Late Pleistocene times have been linked to changes in ocean circulation, but their causes remain uncertain. One of the largest such events in the Holocene occurred between 8,400 and 8,000 calendar years ago,, (7,650–7,200 14C years ago), when the temperature dropped by 4–8 °C in central Greenland and 1.5–3 °C at marine, and terrestrial, sites around the northeastern North Atlantic Ocean. The pattern of cooling implies that heat transfer from the ocean to the atmosphere was reduced in the North Atlantic. Here we argue that this cooling event was forced by a massive outflow of fresh water from the Hudson Strait. This conclusion is based on our estimates of the marine 14C reservoir for Hudson Bay which, in combination with other regional data, indicate that the glacial lakes Agassiz and Ojibway, (originally dammed by a remnant of the Laurentide ice sheet) drained catastrophically ∼8,470 calendar years ago; this would have released >1014 m3 of fresh water into the Labrador Sea. This finding supports the hypothesis,, that a sudden increase in freshwater flux from the waning Laurentide ice sheet reduced sea surface salinity and altered ocean circulation, thereby initiating the most abrupt and widespread cold event to have occurred in the past 10,000 years.

Provenance of Late Quaternary ice-proximal sediments in the North Atlantic: Nd, Sr and Pb isotopic evidence

In order to assess the isotopic characteristics of siliciclastic sediments delivered by the Laurentide, Greenland, Iceland and Fennoscandian ice sheets to the North Atlantic, the Nd, Sr, and Pb isotopic compositions were determined for twenty-six samples of Late Quaternary, fine-grained ( −15) IRD comprising H3 and H6, and that was deposited before and after lower ϵNd IRD in other Heinrich events, could have been delivered to the North Atlantic from the Fennoscandian Ice Sheet, as previous workers concluded, but our data reveal that southeastern margin of the Laurentide Ice Sheet is a viable alternative source for the higher ϵNd IRD.

Contributions of Organic and Inorganic Matter to Sediment Volume and Accretion in Tidal Wetlands at Steady State

Abstract A mixing model derived from first principles describes the bulk density (BD) of intertidal wetland sediments as a function of loss on ignition (LOI). The model assumes that the bulk volume of sediment equates to the sum of self‐packing volumes of organic and mineral components or BD = 1/[LOI/k1 + (1‐LOI)/k2], where k1 and k2 are the self‐packing densities of the pure organic and inorganic components, respectively. The model explained 78% of the variability in total BD when fitted to 5075 measurements drawn from 33 wetlands distributed around the conterminous United States. The values of k1 and k2 were estimated to be 0.085 ± 0.0007 g cm−3 and 1.99 ± 0.028 g cm−3, respectively. Based on the fitted organic density (k1) and constrained by primary production, the model suggests that the maximum steady state accretion arising from the sequestration of refractory organic matter is ≤ 0.3 cm yr−1. Thus, tidal peatlands are unlikely to indefinitely survive a higher rate of sea‐level rise in the absence of a significant source of mineral sediment. Application of k2 to a mineral sediment load typical of East and eastern Gulf Coast estuaries gives a vertical accretion rate from inorganic sediment of 0.2 cm yr−1. Total steady state accretion is the sum of the parts and therefore should not be greater than 0.5 cm yr−1 under the assumptions of the model. Accretion rates could deviate from this value depending on variation in plant productivity, root:shoot ratio, suspended sediment concentration, sediment‐capture efficiency, and episodic events.

Volumetric analysis of a New England barrier system using ground-penetrating-radar and coring techniques

Ground-penetrating-radar (GPR) profiles calibrated with core data allow accurate assessments of coastal barrier volumes. We applied this procedure successfully to the barrier system along Saco Bay, Maine (USA), as part of a sediment-budget study that focused on present-day sand volumes in various coastal, shoreface, and inner-shelf lithosomes, and on sand fluxes that have affected the volume or distribution of sand in these sediment bodies through time. On GPR profiles, the components of the barrier lithosome are readily differentiated from other facies, except where the radar signal is attenuated by brackish or salty groundwater. Significant differences between dielectric properties of the barrier lithosome and other units commonly result in strong boundary reflectors. The mostly sandy barrier sediments allow deep penetration of GPR waves, in contrast to finer-grained strata and till-covered bedrock. Within the Saco Bay barrier system,

Shoreline Analysis and Barrier Island Dynamics: Decadal Scale Patterns from Cedar Island, Virginia

22 \pm 3 \times 10^{6} m^{3}

Dansgaard–Oeschger events: is there a signal off the Hudson Strait Ice Stream?

of sediment are unevenly distributed. Two-thirds of the total barrier volume is contained within the northern and southern ends of the study area, in the Pine Point spit and the Ferry Beach/Goosefare complex, respectively. The central area around Old Orchard Beach is locally covered by only a thin veneer of barrier sand, averaging >3 m, that unconformably overlies shallow pre-Holocene facies. The prominence of barrier-spit facies and the distribution pattern of back-barrier sediments indicate that a high degree of segmentation, governed by antecedent topography, has affected the development of the Saco Bay barrier system. The present-day configuration of the barrier and back-barrier region along Saco Bay, however, conceals much of its early compartmentalized character.

Fine scale sediment structure and geochemical signature between eastern and western North Atlantic during Heinrich events 1 and 2

] Hulbe et al. [2004] argue that the original binge-purge model of their coauthor MacAyeal [1993a, 1993b]is not appropriate for Heinrich events but that a new ice-shelf-collapse mechanism may work. We believe that thenew collapse mechanism disagrees with important dataand that MacAyeal’s original model remains viable afterappropriate modifications. We have enjoyed a fascinatingdiscussion with Hulbe et al. on this topic, which isstimulating our thinking and research, and we presentsome of the arguments here for a wider audience.[

Late Quaternary stratigraphy, chronology, and depositional processes on the slope of S.E. Baffin Island, detrital carbonate and Heinrich events: Implications for onshore glacial history

Abstract Nebel, S.H.; Trembanis, A.C., and Barber, D.C., 2012. Shoreline analysis and barrier island dynamics: Decadal scale patterns from Cedar Island, Virginia. Aerial photography, topographic maps, high-resolution satellite imagery, and global positioning system (GPS) data were compiled in ArcMAP™ and analyzed using the Digital Shoreline Analysis System (DSAS) to determine decadal trends of shoreline movement on Cedar Island, Virginia. Shoreline retreat rates for Cedar Island had an alongshore average of −4.1 m/y based on simple endpoint analysis (1852–2007), while the short-term (1994–2007) retreat rates increased to −12.6 m/y. Retreat statistics were further calculated for the time intervals 1852–1910 (−5.1 m/y), 1910–62 (−3.5 m/y), 1962–80 (−3.9 m/y), 1980–94 (−6.5 m/y), 1994–2002 (−12.4 m/y), and 2002–06 (−13.8 m/y). This analysis indicates that retreat of the Cedar Island shoreline has been accelerating with a notable increase in rate within the years 1980 to 1994. Additionally, the shoreline data confirms that the orientation of the Cedar Island shoreline has rotated through time.