Late Holocene sea-level changes in eastern Québec and potential drivers

Abstract

Late Holocene sea-level changes can be reconstructed from salt-marsh sediments with decimetre-scale precision and decadal-scale resolution. These records of relative sea-level changes comprise the net sea-level contributions from mechanisms that act across local, regional and global scales. Recent efforts help to constrain the relative significance of these mechanisms that include sediment dynamics and isostasy, which cause relative sea-level changes via vertical land motion, ocean-atmosphere processes that influence regional-scale ocean mass redistribution, and ocean-cryosphere and steric interactions that drive global scale ocean-volume changes. There remains a paucity of high-resolution Late Holocene sea-level data from eastern Canada. This precludes an interrogation of the mechanisms that define sea-level changes over recent centuries and millennia in a region sensitive to oceanic (Atlantic Multidecadal Variability, Atlantic Meridional Overturning Circulation), atmospheric (North Atlantic Oscillation, Arctic Oscillation) and cryospheric (ice-mass balance) changes. We present new relative sea-level data that span the past three millennia from Baie des Chaleurs in the Gulf of St. Lawrence generated using salt-marsh foraminifera supported with plant macrofossil analyses. The accompanying chronology is based on radiocarbon and radionuclide analyses, which are independently verified using trace metal and microcharcoal records. Relative sea level has risen at a mean rate of 0.93 ±1.25 mm yr-1 over the past ~1500 years. Residual structure within the reconstruction ('internal variability') has contributed up to an additional 0.61 ±0.46 mm yr-1 of shortlived RSL rise prior to 1800 CE. Following a sea-level low stand during the Little Ice Age, acceleration in relative sea-level rise is identified between 1800 and 1900 CE within the estimates of internal variability and from 1950 CE to present in both the secular and residual trends. Phases of relative sea-level changes in the Gulf of St. Lawrence are concomitant with periods of glacier mass loss following the Little Ice Age, phase periods of the North Atlantic Oscillation and the Atlantic Meridional Overturning Circulation and Northern Hemisphere warming. Quantifying the individual effects of these different mechanisms is important for understanding how ocean-atmosphere processes redistribute ocean-mass upon larger scale background ocean-volume changes.

Common Era sea-level budgets along the U.S. Atlantic coast

“…The 2274 individual data points in the database use proxies such as foraminifera, diatoms, testate amoebae, coral microatolls, archaeological evidence, and sediment geochemistry. We have updated the database (Supplementary Data) from Kemp et al (2018) to include 390 new RSL data points from northern New Jersey, USA (this study); Croatia 56 ; French Polynesia 57 ; Israel 58 ; Quebec 59 ; Connecticut 25 ; Maine 25 ; and Nova Scotia 25 . We compared the new northern New Jersey record with other published records along the U.S. Atlantic coast from southern New Jersey (Leeds Point and Cape May Courthouse 14 ), New York City 15 , Connecticut 60 , and North Carolina 45 to examine regional variability in magnitudes and rates of past RSL change, as well as variability in regional Common Era sea-level budgets.…”

Reliability of mangrove radiocarbon chronologies: A case study from Mahé, Seychelles

“…Therefore, where preserved, above-ground plant macrofossils are likely to closely record the age of sediment deposition. In salt marshes – which inhabit the same ecological niche as mangroves but in temperate climates – leaves, seeds and depth-specific rhizomes are commonly preserved and are used to construct high-resolution age models for decimetre-scale RSL reconstructions (Barnett et al, 2019; Kemp et al, 2018; Long et al, 2012). Mangrove plant macrofossils have provided reliable sequences of radiocarbon ages in some locations (Grand Pre et al, 2012; Monacci et al, 2009; Wooller et al, 2007), particularly sites with high sedimentation/burial rates.…”

Modelling Coastal Flood Propagation under Sea Level Rise: A Case Study in Maria, Eastern Canada

“…The observed rate of sea level rise is both the result of eustatic sea level variations and regional glacio-isostatic adjustments (GIA) along Atlantic Canada [5,[42][43][44], varying between −1 and −4 mm/year in the Gulf of St Lawrence [5,45]. The relative sea level has risen at a mean rate of 0.93 ± 1.25 mm/ year over the past ~1500 years in the Chaleur Bay and GIA was a significant contributor to this rate [79]. In recent decades, sea level rise has increased at a mean rate of 4.06 mm/year at the Belledune tide gauge between 1964-2014 ( Figure 1a).…”