Challenges in relative sea-level change assessment highlighted through a case study: The central coast of Atlantic Patagonia

There are areas in the world where our understanding of past sea-level changes is less robust than in others. This
is partly due to the difficulty past investigators had adopting i) high-resolution elevation measurement techniques
(largely available only in the last decade) and ii) standardized methodological approaches to reconstruct
past relative sea levels starting from field measurements. The central coast of Atlantic Patagonia (Argentina),
preserves a unique succession of coastal landforms, which scientific investigations suggest to have been formed
discontinuously since at least marine isotope stage 11 up to the Holocene. Patagonian coastal deposits (in
particular raised beach ridges, marine terraces and river mouth terraces) and erosional landforms (slope angles,
marine notches) were studied in the past with the aim of reconstructing relative sea-level changes and provide
geological evidence to constrain geophysically based models for an area affected by significant vertical displacement
due to isostatic adjustment and possibly by tectonic uplift. So far, there is no general agreement about
the interpretation of Patagonia landforms and deposits in terms of sea-level index points. This is certainly a gap
within a planetary scale overview of sea-level change and represents an obstacle for the construction of a sound
model of glacial isostatic adjustment for the area. In this paper we critically analyse previous works on sea-level
change along the central coast of Atlantic Patagonia and highlight the major sources of uncertainty, including
choices about calculating past relative sea levels from the elevation of indicators and the vertical datum used. We
also provide a comparison between different vertical datums (tidal, gravimetric and geodetic) at a real site
(Puerto Deseado) where Differential Global Positioning System measurements were performed by our team in
2016, and address the problem from a trans-disciplinary point of view. In order to obtain accurate sea-level
change estimates in the area, we suggest the use of a large spectrum of sea-level markers with well-defined
indicative meanings and the adoption of specific technical choices capable of minimizing instrumental errors.

This work was made possible thanks to the funding of the University
of Pisa (Progetto Ateneo 2007, Leader G. Zanchetta and Progetto
Ateneo 2015, Leader G. Zanchetta) and of MIUR (PRIN 2008, Leader G.
Zanchetta).