PhD project, paleohurricanes, Mont Blanc, France

A PhD project on "Plurimillenial recurrence patterns of Super-Hurricanes in the Caribbean revealed by coastal sediments" is being offered by the Université Savoie Mont Blanc, France.

Description

Given hurricane Irma (31 August-11 September 2018) was the most powerful Atlantic Ocean hurricane in recorded history, it is essential to examine the past decadal- to millennialscale variability of hurricane activity in order to answer the questions: (1) Is Irma a new kind of kind of super-hurricanes triggered by the global warming? (2) Was there in the past a direct link between the frequency of most extreme hurricanes and global climatic changes?

The Caribbean is frequently hit by hurricanes and uncertainties about the risk of hurricanes and related marine submersions are aggravated by the lack of knowledge about return periods of most extreme events. Relatively few works have been published about the hurricane history and in particular most lagoons and salt marshes remain unexplored in this area from a geological point of view. Moreover there are still debates whether lagoons geological records could be interpreted as consequences of tsunamis or hurricanes.

To address these issues, this project aims at tackling the challenge of reconstructing the hurricane history in the area of the Caribbean and downstream, assessing the recurrence time and triggering factors of the extreme hurricanes. To reach these goals we propose a multi disciplinary approach combining geomorphological analysis from satellite images with very shallow water seismic profiling and sediment cores in 12 coastal lagoons in the Northern part of the Caribbean Sea, in order to successively:

- reconstruct the coastal evolutions during the last millenaries;
- decipher tsunami-related and hurricane-related sediment records in coastal lagoon;
- reconstruct the Holocene marine submersion history during the last millenaries;
- evaluate the frequency of the most extreme hurricane events in relation to past and present-day climate change;
- discuss the frequency of future extreme hurricane events in the light of hurricane history and projected climate changes.

It is essential to examine the past decadal- to millennialscale variability of hurricane activity in order to determine both the frequency of the most extreme events in relation to the climate evolution and in what extent Irma-like super hurricanes should become the standard of hurricane strength in a warming world.

Taking into account the expected sea-level rise at the end of the century, together with regionally increased storm activity and the expected population increase in coastal zones in the next decades, marine submersion frequency and associated damages are expected to increase. Anticipating and managing future marine submersions is thus a priority.

To improve our preparedness, magnitude and probability of occurrence of super-hurricanes and related submersions must be known over the long term, i.e. longer than the last few decades known with instrumental data. Geological data offer opportunities to reconstruct long-term records of intense events hence prolonging the documented record far beyond the direct observation period. This would provide a better understanding of the possible regional and local long-term trends of storm activity as they relate to past climatic conditions. Usually, reconstructions of past hurricane events in coastal environments have been made by identifying the recurrence of coarse-grained overwashes and associated deposits.

Objectives

The main objective of this PhD project is to identify super-hurricanes recurrence patterns using historical and geological data from a collection of lagoon sediment-fill located in the Northern part of the Caribbean Sea (Anguilla, Saint-Martin, Saint-Barthélemy, Antigua, Barbuda). This project is based on multiple sediment cores sampled in 12 lagoons in March 2018. The PhD student will follow a high-resolution multi-proxy approach associating sedimentological, geochemical, and faunistic data. On the other hand, a chronology will be based on short-lived radionuclides and radiocarbon ages.

The scientific objectives of this PhD are:

- Reconstruction of coastal evolutions during the last millenaries from sediment records in 12 coastal lagoons in the Northern part of the Caribbean Sea;
- Deciphering tsunami-related vs. hurricane-related sediment records in coastal lagoon;
- Reconstruction of the Holocene marine submersion history (related to both tsunamis and hurricanes) in the Caribbean from coastal lagoon sediments;
- Evaluating the frequency of the super-hurricane events in relation to past and present-day climate changes;
- Discussing the frequency of future super-hurricane events in the light of past hurricane and climate histories and projected climate change.

Methodology and planning

The methodology used during this PhD is subdivided in three domains: Geomorphology, Stratigraphy, Sedimentology. Stratigraphy and Sedimentology are based on two field campaigns. The first field campaign (March 2018) already allowed sampling 38 short cores (< 2 m) in 12 lagoons located in 6 islands (Antigua, Barbuda, St Martin, St Barthélémy, Anguilla and Scrub Island). The second field campaign will be conducted in 2019 and will consist in seismic exploration and long-core sampling.

1- Geomorphology: A morphological analysis using high-resolution satellite data and CNES Pleiade imagery to create high resolution DEMs (2 m horizontal resolution) by using CNES/IGN Euclidium and IGN Micmac numerical codes.

2- Stratigraphy: We will apply an original approach combining very high-resolution (VHR) seismic stratigraphy and multiple coring transects. The seismic tools (LIENSs laboratory) have vertical resolution of 20 cm and can evidence acoustic impedance changes related to small grain size changes such as the transition between fine and coarse silts or to the presence of shell lags. The seismic exploration will reveal the internal architecture of the lagoon sediment fills and ideal coring sites. Sediment cores will be sampled along seismic profiles, by using a light Uwitec corer (EDYTEM, Université Savoie Mont Blanc, EQUIPEX CLIMCORE). This corer can be deployed from a small boat and allows 6 meters-long sediment penetrations.

3- Sedimentology: A multiproxy approach will be conducted, and will include:

- Analysis of mineralogy, grain size, colour, density, organic and water content to understand sediment dynamics.
- Macro and micropaleontology to reconstruct the paleoenvironmental evolution of the coastal systems since the Holocene marine transgression.
- Analysis of benthic foraminifera as indicator of the source of the displaced material to decipher between tsunami hurricane -related deposits.
- Continuous high-resolution geochemical analyses using an XRF scanner, associated with geochemical analyses and statistical analysis to calibrate the XRF signal to track marine deposits.
- Mid-infrared spectrometry for both organic and mineral fraction characterization.
- Chronology: AMS 14C dating of terrestrial macroremains and shells, short-lived radionuclides (210Pb, 137Cs). Any 14C reservoir age on shells will be also determined.

Working plan

Y1: Field trip 1: acquisition of short cores (already done), sedimentological, geochemical and geochronological analysis on cores.
Y2 field trip 2: seismic survey and long cores on selected sites, multiproxy analysis of cores and chronostratigraphic studies with associated geophysical data analysis.
Y3: Development of long-term hurricane catalogue and publication of results.

Keywords

Hurricane, Marine submersion, Climate change, coastal lagoon, sediment.

Requirements

The student selected for this PhD needs to have a strong background in geology, geophysic and geochemistry. He/she will be selected on the base of his/her scholar results. He/she will have to present a dossier with his/her marks, a letter of motivation and of recommendation from his/her previous supervisor, and other teachers. After a selection of the better candidates from their dossier, we will interview them to select the best candidate.

The candidate must have an open mind and be interested in multidisciplinary research. He/She must collaborate with different partners and need to be able to adapt easily. He/She must be meticulous and like manual work for the core study. First of all, we expect a serious student motived and involved in his/her work.

Each PhD is a unique human adventure with marvellous moment and some harder ones. It is a way to transmit important value around research, rigor, integrity, as well as knowledge and a way of working. It is interesting to observe the evolution of a research project when a student is making the subject his. It is interesting to support a young scientist in his first steps into the world of research. It is also a wonderful way to collaborate with other scientific partners. Supervising a Ph-D is a very rich experience.

Partnership

This PhD project will be realized in a strong partnership between three French laboratories (IPGP, LIENSS, EDYTEM) and one Australian University (University of New South Wales, Sydney) in the framework of an early beginning ANR project (CARQUAKES) on Lesser Antilles Arc, lead by Nathalie Feuillet (IPGP).

IPGP lab (Nathalie Feuillet) lab is a national leader in earth sciences with a strong experience in the Lesser Antilles after working in earth observatories in Martinique and Guadeloupe (French Antilles).

LIENSS lab (Eric Chaumillon) has extensive experience with very high-resolution stratigraphy and sedimentology in coastal environments to identify climatic and geological events such as storms deposits.

EDYTEM lab (Pierre Sabatier) is one of the French leader laboratories in the analysis of lacustrine sediments to reconstruct past environmental and climate changes in mountain and coastal areas.

Catherine Chagué (University of New South Wales, Sydney) is an internationally recognised specialist in the field of tsunami deposits.

International context

Billions of people are in the path of tropical cyclones, and regional storm activity and population in coastal zones are both expected to increase. Along many coasts around the world, uncertainties about the risk of hurricanes and related marine submersions are aggravated by the lack of knowledge about return periods of most extreme hurricanes. Moreover, in a context of global warming, it is essential to understand the relationships between those events and climate changes.

Paleotempestology is a new field of research that emerged during the last decades and it provided insights about the intensity of past hurricanes and the extent and frequency of major past flooding events. Pioneering works have been conducted along the East US coasts and paleotempestology is now applied to many coasts around the word. Nevertheless, it appears that many sediment records are still not analysed and many coasts where historical archives are absent left unexplored.

In the Caribbean, relatively few works have been published about the hurricane history and many lagoons left unexplored. Moreover they are still debates concerning some boulder ridges and sand sheets in lagoons, which may be interpreted as consequences of tsunamis or hurricanes. Consequently there is a need for reconstructing the hurricane history in the area of the Caribbean and for evaluating the frequency of the most extreme hurricane events in relation to past and present-day climate changes.

One of the hardest obstacles in analysis of sedimentological records of past marine floods is related to absolute chronology of events that occurred during the last centuries and our expertise in geochronology will be very useful to deal with this issue.

Position of the project in relation with the MOPGA scientific domains

The three main topics of research prioritized in MOPGA are Earth system sciences, Climate change and sustainability sciences, Energy transition. This PhD project depends on the first two topics.

This project is clearly related to earth system sciences because all methods coming from this scientific field and all involved researchers are geologists. The first objective of this project is to show if extreme hurricane events, such as Irma, already existed in the past and if they are likely to be the standard in the future? For this we will develop a retro-observation method based on natural archive of past hurricanes and climate changes.

Taking into account the expected sea level rise at the end of century, together with regionally increased storm activity and the expected population increase in coastal zones in the next decades, marine submersion frequency and associated damages are expected to increase. Anticipating and managing future marine submersions is thus a priority and this project will bring critical information for future demography, economics strategies. Therefore this project responds also to the second topics prioritized in MOPGA.

Eligibility

You are eligible to apply for the PhD/Doctorate program "Make Our Planet Great Again" if:

- You have a Master's degree or you will pass a Master's degree before 31 August 2018
- You have lived in France for less than 90 days since 1 April 1 2016
- You are exclusively a foreign national

Applications

Application deadline is 22 April 2018.

Please send your CV and a letter of motivation to the following contacts: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

Further information

Read the official description here: https://doctorat.campusfrance.org/CF201812488

Informal questions can be sent to Pierre Sabatier: This email address is being protected from spambots. You need JavaScript enabled to view it.