AutogenicDominant

MixingAmplifiedAutogenic

MixingDampenedAllogenic

AllogenicDominant

Width Drown

Width Drown

HeightDrown

HeightDrown

MixingOffset

Autogenic

12 10 8 6

-20

-40

-60

Age (kyrs BP)

Ele

vation

(m

bel

ow M

SL)

A

B

C

D

E

F

Mel

twat

er P

uls

e 1B

8.2

kyr

ris

e

Mig

ration

Aggra

dat

ion

Aggra

dat

ion

Aggra

dat

ion

Mig

ration

Mig

ration

Autogenic Deposition: Wavelength and Volume vs. Slope

Seabed Profiles of Relict Barriers Around the World

Response to 200 yr Pulse in Rate of Sea Level Rise

Abstract

Autogenic & Allogenic Interaction: Deposition During Rapid Sea Level RiseAutogenic Dominant Mixing: Amplified Autogenic

Mixing: Offset Autogenic Mixing: Dampened Allogenic Allogenic Dominant

40 m

0 m~2 km ~2 km

Hastings Bank Seabed Profile (after Mellet et al., 2012)

4 km

30 m

0 m

Barrier

4 km

Long Island Seabed Profile (after Rampino and Sanders, 1980)

~5 km

4 km

New Jersey Seabed Profile (after Nordfjord et al., 2009)

*Note: Profile approximately diagonal to cross-shore

55 m

80 m

~9-10 km*

4 km

42 m

74 mSouth Africa Seabed Profile (after Pretorius et al., 2016)

Sub 1 km wavelengths

0 m

20 m4 km

W. Florida Seabed Profile (after Locker et al., 2003)

Wavelength

Overwash

Stranded Barrier Sand

Barrier

~7 km

Barrier Remnant

Idealized Seabed Profile

Barrier

0 m

Back Barrier/Overwash Seds

Modern Barrier

Chronology of HoloceneDrowned Barrier Deposits

Age (based on 14C and OSL dating) of drowned barrier deposits and elevations, reproduced and modified from Mellet and Plater (2018). Generalized sea level curve modified from Gornitz (2007) after Fairbanks (1989).

A. Adriatic Sea - Storms et al. (2008)B. Kattegat, South Scandinavia - Bennike et al. (2000)C. Heald Bank, Gulf of Mexico, USA - Rodriguez et al. (1999)D. Rhine-Meuse, Netherlands - Hijma et al. (2010)E. Hastings Bank, English Channel, UK - Mellet et al. (2012)F. Old Rhine, Netherlands - Rieu et al. (2005)

Pulse rate of rise (mmy/yr)

Tim

ing

rela

tive

to s

tart

of a

utog

enic

cyc

le (

yrs)

Ocean Shoreline

BackbarrierShoreline

Shoreface Toe

Autogenic DepositionAutogenic Cycle - Periodic Retreat

Where age control is available for drowned barrier deposits, clustering around meltwater pulses could suggest a relationship, but in many cases barrier deposits are produced several thousand years later. How is this possible? What are the implications for modern barriers experiencing increased rates of sea level rise?

Overwash

Shoreface Fluxes

Long Term Risks: Novel Barrier Island Retreat Behaviors Arising from Increasing Rates of Sea Level Rise

Daniel J. Ciarletta1, Jorge Lorenzo-Trueba1, & Andrew D. Ashton2

1Department of Earth and Environmental Studies, Montclair State University, Montclair, NJ 07043

The hazards faced by retreating barrier island systems to the increased rates of sea level rise predicted over the coming century and beyond lacks historic precedent. Consequently, exploration of the sedimentological record can provide key insights into how barrier systems might behave in the future. Continental shelves around the world preserve records of former barriers as relict deposits, providing a window into past behaviors. These relict barrier deposits are usually considered to originate from purely allogenic processes, or external environmental forcing, with barrier abandonment typically attributed to episodes of increased rate of sea level rise. However, using a cross-shore morphodynamic model, we show that the internal dynamics of migrating barriers can also result in autogenic deposition of relict sediments even under a constant rate of sea level rise. Subsequently, we propose that allogenic forcing from sea level rise and autogenic forcing from internal dynamics might interact to produce novel barrier retreat behaviors, with the potential to be recorded on the seabed by relict deposits. We model barriers through a range of scenarios with interacting autogenic and allogenic forcing, showing that the morphology of deposits might be used to infer the relative influence of external and internal processes. Intriguingly, our results demonstrate that the internal dynamics of barriers can both amplify and dampen losses of shoreface sediment to the seabed during increased rates of rise, in some cases with internal processes increasing the risk of barrier destruction. Future classification of relict deposits in the field could help explain if and when these allogenic/autogenic interactions have taken place, revealing long term hazards to modern barrier systems that have not previously been described.

2Geology and Geophysics Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543

Research possible in part through NSF Award #1518503, Coastal Processes and Human Response to Shoreline Change

Dissertation Committee: Dr. Sandra Passchier, Dr. Mark Chopping, and Charles Dill (AOSS Inc.)

Additional thanks to MSU colleagues for their time and support:Jesse Kolodin, Arye Janoff, William Anderson, Christopher Tenebruso, and Isamar Cortes