# Morphogenesis of the Holocene coastal landforms on Sumba Island, Indonesia

Denovan Chauveau, Kevin Pedoja, Christine Authemayou, Laurent Husson, Gino de Gelder, Sonny Aribowo, Mary Elliot, Anne-Morwenn Pastier, Danny Hilman Natawidjaja, Vera Christanti Agusta, et al.

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Denovan Chauveau, Kevin Pedoja, Christine Authemayou, Laurent Husson, Gino de Gelder, et al. Morphogenesis of the Holocene coastal landforms on Sumba Island, Indonesia. Journal of Asian Earth Sciences: X, 2025, 14, 10.1016/j.jaesx.2025.100208. hal-05284217

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# Morphogenesis of the Holocene coastal landforms on Sumba Island, Indonesia

Denovan Chauveau<sup>a, *, 1</sup> <sup>1</sup>D, Kevin Pedoja<sup>b, 1</sup>, Christine Authemayou<sup>a</sup>, Laurent Husson<sup>c</sup>, Gino de Gelder<sup>c, d</sup>, Sonny Aribowo<sup>c, d</sup>, Mary Elliot<sup>e</sup>, Julius Jara–Muñoz<sup>f</sup>, Anne-Morwenn Pastier<sup>g</sup>, Danny Hilman Natawidjaja<sup>d</sup>, Vera Christanti Agusta<sup>d, e</sup>, Sri Yudawati Cahyarini<sup>d</sup>

## ARTICLE INFO

**Keywords:**

Coastal terrace

Holocene

Relative sea level

Uplift

South-East Asia

## ABSTRACT

Coastal terraces, whether erosional, depositional, or bio-constructed, have been widely used to quantify Late Cenozoic vertical deformation and relative sea-level changes. Here, we review and investigate the Holocene coastal terraces of Sumba Island, Indonesia. We describe fifteen coastal sites, evenly distributed between the South and North coasts. The terraces are Holocene age, based on ¹⁴C and U/Th ages. We show that the preservation of coastal terraces in Sumba is favoured on the leeward coast (North). Holocene and older Pleistocene coastal terraces are almost absent on the windward coast (South), although modern coral reefs almost ubiquitously thrive. The morphology and the nature of the bedrock varies between the two sides of the island: while sequences of earlier Pleistocene coral reef limestones dominate in the North, Miocene/Pliocene tuffs and pelagic carbonates outcrop on the southern coast. The elevations of the Holocene inner edges range from 2.4 ± 0.7 to 6.9 ± 0.7 m above the present mean sea level. Despite disparate uplift rates, the three preserved windward terraces (out of the seven sites investigated) generally have a higher inner edge than leeward terraces. We conclude that neither glacio-eustatic oscillations, vertical deformation rates nor hydrodynamics by themselves can explain the variability in inner edge elevations on Sumba, but only a complex combination of these processes. Finally, our study serves as a solid basis for future investigation of the Holocene landforms of the island of Sumba and other similar tropical coastal zones.

## 1. Introduction

One of the keys to approximating future sea-level changes is the study of past sea-level fluctuations (e.g., Rohling et al., 2019; Creel et al., 2024). This can be achieved by geochemical proxies (e.g., benthic foraminifera, Waelbroeck et al., 2002) and analyses of fossil coastlines (Pedoja et al., 2011). However, while the latter are well-documented (e. g., Pedoja et al., 2014; Rovere et al., 2023), the full understanding of their morphogenesis and evolution remains an ongoing research topic

(e.g., de Gelder et al., 2022; Maxwell et al., 2025; Woodroffe, 2025).

Coastal terraces are geomorphic features found along rocky, sedimentary, or reefal platforms. They are limited landward by fossil sea cliffs (Lajoie, 1986) and often carved by notches (Antonioli et al., 2006). Coastal terraces are typically organized in stacked, staircase sequences, which are the fingerprints of the Late Cenozoic sea-level changes on uplifting/subsiding coasts (e.g., Lajoie, 1986; Murray-Wallace and Woodroffe, 2014). Owing to their recent genesis, emerged Holocene coastal terraces are generally smaller, less pervasive, but better

<footnote><sup>a</sup>Geo-Ocean, Univ Brest, CNRS, Ifremer, UMR6538, F-29280 Plouzane, France</footnote>

<footnote><sup>b</sup>Normandie Univ, Unicaen, Unirouen, CNRS, M2C, 14 000 Caen, France</footnote>

<footnote><sup>c</sup>ISTerre, CNRS, IRD, UMR 5275, Université de Grenoble Alpes, Grenoble, France</footnote>

<footnote><sup>d</sup>Research Organization of Earth Sciences and Maritime, National Research and Innovation Agency, Bandung, Republic of Indonesia</footnote>

<footnote><sup>e</sup>LPG, CNRS, UMR 6112, Université de Nantes, Nantes, France</footnote>

<footnote><sup>f</sup>Faculty of Civil Engineering, Hochschule Biberach, 88400 Biberach an der Riß, Germany</footnote>

<footnote><sup>g</sup>LaROUSTe: Laboratoire Radical et Oblique des Urgences en Science de la Terre, Poitiers, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: Denovan.Chauveau@ifremer.fr (D. Chauveau).</footnote>

<footnote n="1">¹ Denovan Chauveau and Kevin Pedoja contributed equally to this paper and share first authorship.</footnote>
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Sumba Island (Indonesia) and studied Holocene coastal sites. A) Geodynamics of SE Asia and location of Sumba Island. Plate velocities indicated concerning Eurasia plate are from Nugroho et al. (2009), elevation data from the Shuttle Radar Topography Mission (SRTM), and bathymetry data from the General Bathymetric Chart of Oceans (GEBCO). B) Geological map of Sumba Island showing the distribution of studied sites, the shaded relief with main geological units, faults, and drainage lines. Fold axes are deduced from the structural measurement from Authemayou et al. (2022).</figcaption></figure>

preserved than their Pleistocene counterpart (e.g., Pirazzoli, 1994). Moreover, Holocene coastal terraces, landforms, and features often exhibit a seamless continuum extending towards the present-day shoreline, offering a relatively continuous history of local sea level and tectonic movements over the past ~ 12 ka (Vacchi et al., 2016, 2025; Rovere et al., 2018; Hijma et al., 2025).

Sumba Island (Indonesia) is renowned for its well-documented sequence of emerged Pleistocene coastal terraces (Jouannic et al., 1988; Pirazzoli et al., 1991, 1993; Hantoro, 1992; Bard et al., 1996; Nexer et al., 2015; Authemayou et al., 2022; de Gelder et al., 2023; Chauveau et al., 2021a, 2021b, 2024a), but very few studies focused on their Holocene counterparts. Yet, Sumba Island features both a leeward (South) and a leeward (North) coast each and variable uplift rates (Effendi and Apandi, 1993; Nexer et al., 2015) that permit investigating the morphogenesis of coastal terraces. Here, we study the lowermost

coastal terraces, assigned to the Holocene on the basis of their morphological characteristics and on a compilation of previous and new dated samples. Following the description of 15 coastal sites, including 12 previously unexplored, and their regional significance, we investigate the contrasted preservation state of coastal terraces between the leeward northern and windward southern coasts and what impact this might have on sea-level reconstructions or local land movements.

## 2. Sumba Island

### 2.1. Geodynamics

Sumba Island, Indonesia, is the 200-km long and 80-km wide (Fig. 1A) emergent portion of the Sumba Ridge, an isolated tectonic block of crystalline basement located half-way between the Java-Sunda
<caption>**Table 1**</caption>

Dating summary of coastal Holocene deposits and bioconstructions from Sumba Island. The elevation datums are given above: LT (Low tide; Jouannic et al., 1988); MSL (mean sea level; Pirazzoli et al., 1991, 1993; Chauveau et al., 2021a); MLWS (mean low water spring; Bard et al., 1996); HT (high tide; Authemayou et al., 2022). All elevations at site 13 were remeasured at 1.1 ± 0.5 m above pmsl.

<table><thead><tr><th rowspan="2">Reference</th><th colspan="10">Sample information</th><th colspan="10">Radiocarbon age</th><th colspan="10"><sup>230</sup>Th/U chemistry</th></tr><tr><th>Samples</th><th>Species</th><th>Sampling information</th><th>Site</th><th>Longitude<br>(E)</th><th>Latitude<br>(N)</th><th>Elevation<br>(m)</th><th>datum</th><th>Calcite<br>(%)</th><th>Aragonite<br>(%)</th><th>Age BP<br>(yr)</th><th>Age BP calibrated<br>(yr)</th><th><sup>238</sup>U<br>(µg/g)</th><th><sup>232</sup>Th<br>(ng/g)</th><th>(<sup>234</sup>U/<sup>238</sup>U)<br>(<sup>230</sup>Th/<sup>238</sup>U)</th><th>Age BP<br>uncorrected<br>(yr)</th><th>Age BP<br>corrected<br>(yr)</th><th>(<sup>234</sup>U/<sup>238</sup>U)<br>initial<br>(yr)</th></tr></thead><tbody><tr><td rowspan="2">Jouannic<br>et al.<br>(1988)</td><td>SMB.<br>MDL.1-1-3</td><td>–</td><td>in growth<br>position –<br>most likely<br>in situ</td><td rowspan="2">13*<br>Cape<br>Laundi</td><td rowspan="2">–</td><td rowspan="2">–</td><td rowspan="2">3</td><td rowspan="2">LT</td><td rowspan="2">0.5</td><td rowspan="2">99.5</td><td>5070</td><td>–</td><td>2.74 ±<br>0.07</td><td>–</td><td>1.13 ±<br>0.02</td><td>–</td><td>–</td><td>6300 ±<br>200</td><td>–</td></tr><tr><td>SMB.<br>MDL.1–1–1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td rowspan="3">Pirazzoli<br>et al.<br>(1991;<br>1993)</td><td>SMB.<br>MDL.0.1.3</td><td>–</td><td>in growth<br>position? –<br>in situ?</td><td></td><td></td><td></td><td></td><td>1.5</td><td>MSL</td><td>&lt; 1</td><td>&gt; 99</td><td>–</td><td>2.74 ±<br>0.07</td><td>1.13 ±<br>0.02</td><td>–</td><td>–</td><td>6300 ±<br>200</td><td>–</td></tr><tr><td>?</td><td></td><td></td><td></td><td></td><td></td><td></td><td>–</td><td>–</td><td>–</td><td>–</td><td>1920<br>±<br>250<br>5070<br>±<br>200</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>?</td><td></td><td></td><td></td><td></td><td></td><td></td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td rowspan="10">Bard et al.<br>(1996)</td><td>SBA1</td><td>Favidae</td><td>in a fossil<br>detrital<br>ridge – in<br>growth<br>position? –<br>in situ?</td><td></td><td></td><td></td><td></td><td>3</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6210<br>±<br>160<br>2140<br>±<br>140</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA2</td><td>Acropora</td><td></td><td></td><td></td><td></td><td></td><td>3</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>2030<br>±<br>180<br>2080<br>±<br>160</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA3</td><td>Goniastrea<br>retiformis</td><td></td><td></td><td></td><td></td><td></td><td>2</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6230<br>±<br>140<br>2380<br>±<br>160</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA4</td><td>Favites<br>flexuosa</td><td></td><td></td><td></td><td></td><td></td><td>2</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6350<br>±<br>160<br>6240<br>±<br>240</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA5</td><td>Goniastrea<br>pectinata</td><td></td><td></td><td></td><td></td><td></td><td>1</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6420<br>±<br>160<br>6330<br>±<br>240</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA6</td><td>Porites</td><td></td><td></td><td></td><td></td><td></td><td>2</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6440<br>±<br>160<br>6330<br>±<br>240</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA7#1</td><td>Porites (micro<br>atoll)</td><td>in situ</td><td></td><td></td><td></td><td></td><td>1.5/<br>2</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6550<br>±<br>160<br>6240<br>±<br>240</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA7#2</td><td>Porites (micro<br>atoll)</td><td></td><td></td><td></td><td></td><td></td><td>1.5/<br>2</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6600<br>±<br>160<br>6240<br>±<br>240</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA8#1</td><td>Porites (micro<br>atoll)</td><td></td><td></td><td></td><td></td><td></td><td>1.5/<br>2</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6650<br>±<br>160<br>6240<br>±<br>240</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>SBA8#2</td><td>Porites (micro<br>atoll)</td><td></td><td></td><td></td><td></td><td></td><td>1.5/<br>2</td><td>MLWS</td><td>&lt; 1</td><td>&gt; 99</td><td>6700<br>±<br>160<br>6330<br>±<br>240</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr></tbody></table>

(continued on next page)
<table><caption>Table 1 (continued)</caption><thead><tr><th rowspan="2">Reference</th><th rowspan="2">Samples</th><th rowspan="2">Species</th><th rowspan="2">Sampling information</th><th rowspan="2">Site</th><th colspan="4">Longitude</th><th colspan="2">Elevation</th><th colspan="2">Sample composition</th><th colspan="2">Radiocarbon age</th><th colspan="2">$^{230}$Th/U chemistry</th></tr><tr><th>(E)</th><th>(N)</th><th>(m)</th><th>(%)</th><th>(%)</th><th>Calcite</th><th>Aragonite</th><th>Age BP</th><th>Age BP calibrated</th><th>(yr)</th><th>(µg/g)</th><th>(ng/g)</th></tr></thead><tbody><tr><td rowspan="2">Chauveau<br>et al.<br>(2021a)</td><td rowspan="2">17_10</td><td rowspan="2">Pseudodiploria<br>clivosa</td><td rowspan="2">in growth<br>position<br>in situ</td><td rowspan="2"></td><td rowspan="2">120.2207</td><td rowspan="2">-9.5179</td><td rowspan="2">2.0</td><td rowspan="2">MSL</td><td rowspan="2"></td><td rowspan="2">&lt; 1</td><td rowspan="2">&gt; 99</td><td rowspan="2">4970</td><td rowspan="2">5440 ±</td><td rowspan="2">2.37 ±</td><td rowspan="2">1.080</td><td rowspan="2">1.14627 ±</td><td rowspan="2">0.05584 ±</td></tr><tr><td>0.5</td><td>0.00041</td><td>0.00020</td></tr><tr><td rowspan="2">17_13</td><td rowspan="2">Mussismilia<br>leptophylla</td><td rowspan="2"></td><td rowspan="2"></td><td rowspan="2"></td><td rowspan="2">120.2207</td><td rowspan="2">-9.5179</td><td rowspan="2">2.0</td><td rowspan="2">MSL</td><td rowspan="2"></td><td rowspan="2">&lt; 1</td><td rowspan="2">&gt; 99</td><td rowspan="2">2580</td><td rowspan="2">2215 ±</td><td rowspan="2">3.02 ±</td><td rowspan="2">1.281</td><td rowspan="2">1.1404 ±</td><td rowspan="2">0.02199 ±</td></tr><tr><td>0.5</td><td>0.000</td><td>0.0003</td></tr><tr><td rowspan="2">Auchemayou<br>et al.<br>(2022)</td><td rowspan="2">18_12B</td><td rowspan="2">Gastropods</td><td rowspan="2">in situ</td><td rowspan="2"></td><td rowspan="2">118.9706</td><td rowspan="2">-9.5859</td><td rowspan="2">1.0</td><td rowspan="2">HT</td><td rowspan="2"></td><td rowspan="2">&lt; 1</td><td rowspan="2">&gt; 99</td><td rowspan="2">565</td><td rowspan="2">145 ±</td><td rowspan="2">0.0253 ±</td><td rowspan="2">0.979</td><td rowspan="2">1.0989 ±</td><td rowspan="2">0.0337 ±</td><td rowspan="2">4420 ± 130</td></tr><tr><td>0.5</td><td>0.0001</td><td>0.0024</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

<caption>Table 2</caption>

Wave (CAWCR) and tidal (OTPS) conditions for each site studied. All these data are those used in IMCalc (Lorscheid & Rovere, 2019). Acronyms are defined as follows: CAWCR = Collaboration for Australian Weather and Climate Research; OTPS = OSU (Oregon State University) Tidal Prediction Software; Hs = Significant wave height; Tp = Mean period of waves; MAX = maximal value; MIN = minimal value; MHHW = Mean Higher High Water; MHW = Mean High Water; MTL = Mean Tidal Level; MLW = Mean Low Water; MLLW = Mean Lower Low Water. The CAWCR is based on WaveWatch III wave model outputs from 1979 to 2010 on a 0.4 x 0.4-degree global grid.

<table><thead><tr><th rowspan="2">Site</th><th rowspan="2">Coast</th><th rowspan="2">CAWCR conditions</th><th colspan="8">OTPS conditions</th></tr><tr><th>Hs mean (m)</th><th>Hs MAX (m)</th><th>Hs MIN (m)</th><th>Tp mean (s)</th><th>Tp MAX (s)</th><th>Tp MIN (s)</th><th>Tidal range (m)</th><th>MHHW (m)</th><th>MHW (m)</th><th>MTL (m)</th><th>MLW (m)</th><th>MLLW (m)</th></tr></thead><tbody><tr><td>1</td><td>Watu Parunu</td><td>Windward (South)</td><td>1.23 ± 0.37</td><td>3.91</td><td>0.37</td><td>10.93 ± 2.03</td><td>18.53</td><td>4.5</td><td>1.83</td><td>1.09</td><td>0.91</td><td>-0.01</td><td>-0.92</td><td>-1.13</td></tr><tr><td>2</td><td>Tarimbang</td><td></td><td>1.62 ± 0.44</td><td>5.64</td><td>0.57</td><td>12.01 ± 1.83</td><td>18.81</td><td>5.43</td><td>1.81</td><td>1.09</td><td>0.9</td><td>-0.1</td><td>-0.91</td><td>-1.1</td></tr><tr><td>3</td><td>East Wanokaka</td><td></td><td>1.65 ± 0.45</td><td>5.75</td><td>0.58</td><td>11.92 ± 1.84</td><td>18.77</td><td>5.3</td><td>1.77</td><td>1.06</td><td>0.88</td><td>-0.01</td><td>-0.89</td><td>-1.08</td></tr><tr><td>4</td><td>West Wanokaka</td><td></td><td>1.66 ± 0.45</td><td>5.78</td><td>0.58</td><td>11.89 ± 1.84</td><td>18.77</td><td>5.26</td><td>1.77</td><td>1.06</td><td>0.88</td><td>-0.01</td><td>-0.89</td><td>-1.08</td></tr><tr><td>5</td><td>Wakukaka</td><td></td><td>1.7 ± 0.46</td><td>5.92</td><td>0.6</td><td>11.76 ± 1.85</td><td>18.72</td><td>5.08</td><td>1.75</td><td>1.06</td><td>0.87</td><td>-0.01</td><td>-0.88</td><td>-1.07</td></tr><tr><td>6</td><td>Kodi village</td><td></td><td>1.69 ± 0.45</td><td>5.66</td><td>0.6</td><td>11.92 ± 1.83</td><td>18.7</td><td>5.22</td><td>1.73</td><td>1.05</td><td>0.86</td><td>-0.01</td><td>-0.87</td><td>-1.05</td></tr><tr><td>7</td><td>West Kodi</td><td></td><td>1.69 ± 0.45</td><td>5.66</td><td>0.6</td><td>11.92 ± 1.83</td><td>18.7</td><td>5.22</td><td>1.73</td><td>1.05</td><td>0.86</td><td>-0.01</td><td>-0.87</td><td>-1.05</td></tr><tr><td>8</td><td>Mandorak</td><td>Leeward (North)</td><td>1.62 ± 0.43</td><td>5.18</td><td>0.59</td><td>12.15 ± 1.82</td><td>18.74</td><td>5.29</td><td>1.71</td><td>1.04</td><td>0.85</td><td>-0.01</td><td>-0.86</td><td>-1.05</td></tr><tr><td>9</td><td>NE Tambolaka</td><td></td><td>0.97 ± 0.29</td><td>3.77</td><td>0.33</td><td>12.03 ± 2.08</td><td>19.18</td><td>4.11</td><td>1.71</td><td>1.04</td><td>0.85</td><td>-0.01</td><td>-0.86</td><td>-1.06</td></tr><tr><td>10</td><td>Mamboro</td><td></td><td>0.64 ± 0.23</td><td>3.22</td><td>0.19</td><td>11.14 ± 2.45</td><td>19.64</td><td>3.4</td><td>1.72</td><td>1.04</td><td>0.85</td><td>-0.01</td><td>-0.87</td><td>-1.07</td></tr><tr><td>11</td><td>West Sasar</td><td></td><td>0.48 ± 0.24</td><td>2.94</td><td>0.1</td><td>9.01 ± 2.77</td><td>19.69</td><td>2.45</td><td>1.73</td><td>1.05</td><td>0.86</td><td>-0.01</td><td>-0.87</td><td>-1.08</td></tr><tr><td>12</td><td>E Cape Laundi N</td><td></td><td>0.29 ± 0.24</td><td>1.96</td><td>0.01</td><td>4.47 ± 1.38</td><td>20.83</td><td>1.66</td><td>1.76</td><td>1.06</td><td>0.87</td><td>-0.01</td><td>-0.89</td><td>-1.09</td></tr><tr><td>13</td><td>E Cape Laundi S</td><td></td><td>0.29 ± 0.24</td><td>1.96</td><td>0.01</td><td>4.47 ± 1.38</td><td>20.83</td><td>1.66</td><td>1.76</td><td>1.06</td><td>0.87</td><td>-0.01</td><td>-0.89</td><td>-1.09</td></tr><tr><td>14</td><td>Padita, Waingapu</td><td></td><td>0.25 ± 0.24</td><td>1.76</td><td>0</td><td>3.74 ± 1.04</td><td>21.18</td><td>1.6</td><td>1.77</td><td>1.07</td><td>0.88</td><td>-0.01</td><td>-0.89</td><td>-1.1</td></tr><tr><td>15</td><td>North of Cape Undu</td><td></td><td>0.89 ± 0.3</td><td>2.64</td><td>0.21</td><td>10.26 ± 2.15</td><td>18.38</td><td>4</td><td>1.81</td><td>1.08</td><td>0.9</td><td>-0.01</td><td>-0.91</td><td>-1.13</td></tr></tbody></table>
<table><caption>**Table 3**
Elevation of the coastal terraces from Sumba Island. Only sites where a Holocene feature was observed are presented in this table. The location of investigated sites where no Holocene feature was observed can be found in the supplementary data (Table S2). ST: Sedimentary Terrace, MT: Marine Terrace, CRT: Coral Reef Terrace.</caption><thead><tr><th rowspan="2">Site</th><th rowspan="2">Coast</th><th rowspan="2">Lithology</th><th colspan="2">Coordinates</th><th rowspan="2">Nature</th><th rowspan="2">Uplift rate</th><th colspan="2">Elevation above high tide (m)</th><th colspan="3">Elevation above mean sea level (m)</th><th rowspan="2">Width (m)</th><th rowspan="2">Dating technique</th><th rowspan="2">Reference</th></tr><tr><th>Longitude (E)</th><th>Latitude (N)</th><th>m</th><th>Reference used as high tide</th><th>Measurement technique</th><th>Measurement uncertainty (±)</th><th>m</th><th>Total uncertainty (±)</th></tr></thead><tbody><tr><td>1</td><td>Watu Parunu</td><td>Windward (South)</td><td>Miocene/ Pliocene tuffs and pelagic carbonates</td><td>120.5153</td><td>-10.252050</td><td>MT</td><td>0.25</td><td>3.5</td><td>Inner edge / Rocky shore platform</td><td>Laser distance meter</td><td>0.15</td><td>4.4</td><td>0.5</td><td>30 ± 2</td><td>—</td><td>This study</td></tr><tr><td>4</td><td>West Wanokaka</td><td></td><td></td><td>119.443973</td><td>-9.754560</td><td>ST</td><td>0.14</td><td>4</td><td>Limit vegetation / Coastal deposits</td><td>dGPS</td><td>0.08</td><td>4.9</td><td>0.5</td><td>25 ± 5</td><td><sup>14</sup>C & U/ Th</td><td>Authemayou et al. (2022)</td></tr><tr><td>7</td><td>West Kodi</td><td></td><td></td><td>118.967914</td><td>-9.591798</td><td></td><td>0.25</td><td>4.2</td><td></td><td></td><td>0.08</td><td>5.1</td><td>0.7</td><td>150 ± 10</td><td><sup>14</sup>C</td><td>This study</td></tr><tr><td>10</td><td>Mamboro</td><td>Leeward (North)</td><td>Pleistocene coral reef limestone</td><td>119.5942</td><td>-9.349117</td><td></td><td>0.15</td><td>3</td><td></td><td>Barometric altimeter</td><td>0.5</td><td>3.9</td><td>0.7</td><td>50 ± 5</td><td>—</td><td></td></tr><tr><td>11</td><td>West Sasar</td><td></td><td></td><td>119.876192</td><td>-9.339688</td><td></td><td>0.26</td><td>6</td><td></td><td></td><td>0.5</td><td>6.9</td><td>0.7</td><td>200 ± 10</td><td></td><td></td></tr><tr><td>12</td><td>East of the Cape Laundi (N)</td><td></td><td></td><td>120.214252</td><td>-9.505401</td><td>MT / CRT</td><td>0.5</td><td>2.6</td><td>High tide notch</td><td>dGPS</td><td>0.08</td><td>3.5</td><td>0.5</td><td>5 ± 1</td><td></td><td></td></tr><tr><td>13</td><td>East of the Cape Laundi (S)</td><td></td><td></td><td>120;220486</td><td>-9.517467</td><td></td><td>0.5</td><td>0.25</td><td>Limit vegetation / Coastal deposits</td><td></td><td>0.08</td><td>1.1</td><td>0.5</td><td>10 ± 1</td><td><sup>14</sup>C & U/ Th</td><td>Jouannic et al. (1988); Pirazzoli et al. (1991; 1993); Bard et al. (1996); Chauveau et al. (2021a. 2021b. 2024a)</td></tr><tr><td>14</td><td>Padita. Waingapu</td><td></td><td></td><td>120.273051</td><td>-9.640570</td><td></td><td>0.6</td><td>2</td><td>Modern inner edge?</td><td></td><td>0.08</td><td>2.9</td><td>0.5</td><td>10 ± 2</td><td>14C</td><td>This study</td></tr><tr><td>15</td><td>North of Cape Undu</td><td></td><td></td><td>120.800767</td><td>-9.966971</td><td>ST & Notch</td><td>0.3</td><td>1.5</td><td>Limit vegetation / Coastal deposits</td><td>Barometric altimeter</td><td>0.5</td><td>2.4</td><td>0.7</td><td>100 ± 10</td><td>—</td><td></td></tr></tbody></table>
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Variation in the nature and elevation of the Holocene coastal terraces above pmsl alongshore Sumba Island, Indonesia. A) Location of sites. B) Elevation transect of sites 1 to 15. For graphical ease we presented a single synthetic cross section for sites 12 and 13. Grey and green sections, respectively show terraces carved into the Kananggar Fm. and into coral reef limestones. Red asterisks mark sites with potential for relative sea-level reconstructions, i.e., the presence of datable material (corals, bivalve shells, etc.) and geomorphological features that are well exposed and therefore measurable using high-precision techniques. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

trench and the active South Indonesian volcanic arc. The ridge separates the Savu fore-arc basin in the East from the Lombok fore-arc basin in the West (Harris, 2011). Located at the transition of the Java oceanic subduction and the arc-continent collision between the Sunda arc and Australia, Sumba lies in a seismically active zone (Hutchings and Mooney, 2021).

Western Sumba Island corresponds to a large E-W trending, asymmetric anticlinal flexure with a shallow sloping northern flank and a steeper, partly collapsed southern flank structured by gravity faults (Fleury et al., 2009; Authemayou et al., 2018, 2022). Pliocene uplift is higher to the South of the island than to the North (Nexer et al., 2015; Authemayou et al., 2022). During the Quaternary, in the eastern part of the island, folding propagated northwards inducing an apparent maximum Quaternary uplift rate in the northern coast at Cape Laundi and Waingapu bay (Pirazzoli et al., 1991, 1993; Bard et al., 1996; Authemayou et al., 2022). This longitudinal change in deformation pattern can be explained by the lateral transition between the oceanic subduction in the West and arc collision in the East (Authemayou et al., 2022; Husson et al., 2022). An alternative involves the subduction of a seamount beneath Sumba (Fleury et al., 2009) and/or by the subduction of a volcanic ridge, in front of the Australian continental crust (Miller et al., 2021).

Sumba's location in a geodynamically active area makes the island prone to earthquakes. The 1977 Sumba earthquake, a large normal fault earthquake (Mw = 8.3), occurred at the eastern end of the western Java

oceanic trench (Lynnes and Lay, 1988). It produced a ~ 10 m high tsunami on Sumbawa Island, suggesting substantial deformation of the ocean floor and associated fault displacement at shallow depth (Planert et al., 2010). Besides this event, the seismicity of the subduction zone on Sumba Island is moderate (e.g., Jones et al., 2014), historical earthquakes have not produced coastal uplift and co-seismic terraces have not been observed nor described.

## 2.2. Pleistocene coastal landforms

Late Cenozoic emerged coastal sequences (coral reef and marine terraces) are recognized along two-thirds of the North coast of Sumba (Fig. 1B; Verbeek, 1908; Pirazzoli et al., 1991, 1993; Hantoro, 1992; Bard et al., 1996; Fleury et al., 2009; Nexer et al., 2015; Authemayou et al., 2018, 2022; Chauveau et al., 2021a, 2021b, 2024a; de Gelder et al., 2023).

Along the North coast, detailed studies were conducted at Tambo-laka (de Gelder et al., 2023) but mainly at Cape Laundi (Fig. 1B; Pirazzoli et al., 1991, 1993; Murray-Wallace and Woodroffe, 2014; Pedoja et al., 2018). Based on 56 ages (U/Th and ESR), the coral reef terraces (CRTs) of Cape Laundi were correlated to sea-level highstands from MIS 1 (Holocene) to MIS 29 (~1 Ma; Jouannic et al., 1988; Pirazzoli et al., 1991, 1993; Hantoro, 1992; Bard et al., 1996). Relatively constant uplift rates were proposed by several studies: from 0.40 to 0.55 mm a⁻¹ for the last 600 ka (Pirazzoli et al., 1991; 1993) and from 0.20 to
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** The rocky-shore and the low-standing marine terrace at Watu Parunu (Site 1), SE Sumba. A) Watu Parunu location. B-C) Location of site 1. D) Picture of the promontory from the East. E) Interpretation of picture D. F) Picture of the inner edge of the marine terrace on the West side of the promontory. G) Interpretation of picture F. The inner edge of the terrace is at 4.4 ± 0.5 m above pmsl. Satellite images of A, B, and C are from Google Earth (@Maxar Technologies, @TerraMetrics, @DigitalGlobe, Data SIO, NOAA, U.S. Navy, NGA, GEBCO).</figcaption></figure>

0.50 mm a⁻¹ (Bard et al., 1996), although Bard et al. (1996) invoked a recent decrease in uplift rates in order to explain the polycyclic nature of the lower CRTs. Indeed, erosion and reoccupation of pre-existing reefal units by more recent coral colonies formed compound, or polycyclic

CRTs. For example, Pirazzoli et al. (1991, 1993) correlated the three lowest CRTs (CRT I₁, I₂, and I₁₁) to the last three interglacials period (MIS 5, 7 and 9). These authors suggested that an effective marine abrasion during past sea-level fluctuations, superimposed on a constant
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Holocene coastal record at Tarimbang embayment, Site 2, SE Sumba Island. A) Tarimbang location. B) Interpreted picture of the Tarimbang embayment. C) Interpreted picture of the eastern cape. D-E) Interpreted picture of the western cape. The active sea cliff is formed in the Kananggar Fm. Satellite images of A is from Google Earth (@Maxar Technologies, @TerraMetrics).</figcaption></figure>

uplift rate (i.e., 0.5 mm a⁻¹), may have led to reworking of sediments, favouring abrasion, or further developing bioconstructions differing in age by as much as 100 ka on the same CRT. In line, Chauveau et al. (2021a) proposed that the final morphology of the lowest CRTs I₁ and I₂ (inner edges at 6.4 ± 0.5 and 23.2 ± 0.5 m above the present mean sea level, respectively), was acquired during MIS 5c, potentially during MIS 5a and partially during the mid-Holocene highstand (~6 ka) for the distal part of CRT I₁. These reoccupations have been numerically modeled, highlighting that the reef constructions are strongly influenced by the presence of preexisting reefal constructions, creating multiple CRTs for a single MIS (Chauveau et al., 2024a). Furthermore, it has been shown that the morphology of the CRTs at Cape Laundi is smoothed by 1) the interplay between reef growth rates and past sea-level fluctuations, mostly during sea-level regressions following sea-level highstands (Chauveau et al., 2024a), and 2) relatively high continental in situ denudation rates affecting the distal part of the CRTs (Chauveau et al., 2021a). The average continental denudation rate for the whole CRT sequence is 14.7 ± 8.3 mm ka⁻¹ (n = 66), as revealed by the ³⁶Cl cosmogenic nuclide concentration measured in 34 surface samples collected from the unvegetated surfaces of the reefal limestones forming the CRTs (Chauveau et al., 2021a). Chauveau et al. (2021a) concluded that on a given polycyclic CRT, continental denudation can partially strip the thin superficial layer of a young fossil coral reef unit and exhume older corals. These observations indicate that CRTs are not only

bio-constructed terraces, and that erosion (continental and marine) also plays an important role in their morphogenesis. At other sites on the North coast of Sumba Island, uplift rates were deduced from the elevation of MIS 11 CRT (Nexer et al., 2015), and lateral correlation with the sequence of Cape Laundi (de Gelder et al., 2023).

## 2.3. Holocene coastal landforms

Holocene coastal deposits and reef construction were first described on the eastern shore of Cape Laundi (Jouannic et al., 1988) where a 20–30 m wide coral reef platform, including conglomerates, is found at approximately 1.5 m above the present mean sea level (i.e., pmsl; Jouannic et al., 1988). Fossil coral colony samples within this emergent reef have been cross-dated with ¹⁴C and U-series (Table 1; Jouannic et al., 1988; Pirazzoli et al., 1991, 1993; Bard et al., 1996; Chauveau et al., 2021a). 17 ages range from 1920 ± 245 to 6350 ± 160 yr BP (Table 1). Chauveau et al. (2021a) calculated a vertical erosion rate of 430 ± 214 mm ka⁻¹ (n = 2) from this reefal limestone by combining the analysis of ³⁶Cl cosmogenic nuclide concentrations—measured in two samples taken from the top and base of the limestone—with U-series dating of two *in situ* coral conies (samples 17–10 and 17–13; see Table 1).

At Cape Karoka (windward southern coast, Site 4, Fig. 1B) a sequence was recently described (Authemayou et al., 2022). This sequence
<figure><img src="image_7.png" /><figcaption>Fig. 5. The Holocene coastal record on the south-central coast of Sumba Island. A) Location of sites 3, 4, and 5. B) Wanokaka embayment and location of sites 3 and 4. C) Location of Wanokaka Pocket Beach (Site 5). D) Interpreted picture of site 5. E) Interpreted picture of site 3. F) The wave-built terrace at Waiwuang, site 4, with its distal, seaward edge currently under coastal erosion. G) The inner edge of the Waiwuang sedimentary terrace is measured at 4.9 ± 0.5 m above pmsl. Satellite images of A, B, and C are from Google Earth (@Maxar Technologies, @TerraMetrics, @DigitalGlobe, Data SIO, NOAA, U.S. Navy, NGA, GEBCO).</figcaption></figure>

reaches an elevation of 250 m and includes 11 CRTs. On the lowermost CRT, a gastropod shell has been cross-dated using ¹⁴C and ²³⁰Th/U methods from 0.15 to 3.4 ka (sample 18-12B, Table 1, Authemayou et al., 2022). Despite the scarcity of recrystallization of aragonite to calcite, the shell may have undergone post-depositional diagenesis or detrital contamination (Szabo and Rosholt, 1969; Kaufman et al., 1971), which would account for the discrepancies between ¹⁴C and ²³⁰Th/U ages. Regardless, these ages imply that the terrace formed during the Holocene.

## 2.4. Hydrodynamics

The tidal regime of Sumba Island is semidiurnal, with a range of 1.82

± 0.08 m (Nienhuis et al., 2020). Sumba, like many islands, possesses a windward (South) and a leeward (North) coast, each characterized by distinct levels of hydrodynamic energy (Table 2; Schwartz, 2005). The windward southern coast of Sumba is subjected to the relentless force of long-wavelength groundswells with significant wave height (Mean period > 10 s and significant wave height > 1 m, Table 2) and is occasionally affected by tropical cyclones. Conversely, the leeward northern coast experiences waves of shorter wavelength, fetch, or wind swells (Mean period < 10 s and significant wave height < 1 m, Table 2; Butt et al., 2004; Ningsih et al., 2023).
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** The Holocene coastal record at Kodi, SW of Sumba Island. A) Location of sites 6 and 7. B) Detailed mapping of the Kodi area and location of sites 6 and 7. C) Interpreted picture of site 6. D) Interpreted pictures of site 7. The inner edge of the sedimentary terrace is measured at 5.1 ± 0.7 m above pmsl. Satellite images of A and B are from Google Earth (@Maxar Technologies, @TerraMetrics, @DigitalGlobe, Data SIO, NOAA, U.S. Navy, NGA, GEBCO).</figcaption></figure>

# 3. Methods

## 3.1. From field measurements to relative sea-level indicators

A sea-level index point (i.e., SLIP) is a datable feature with a quantifiable relationship to a paleo sea level (Shennan, 2015). This relationship, called the indicative meaning, is often obtained from a modern analog, i.e., from the elevation range covered by the same landform as the fossil one in the modern environment. The quantifiable range of this occurrence, often expressed in terms of tidal levels, is called the indicative range, while the offset between the modern analog and a specified tidal datum is referred to as the reference water level (Shennan, 2015).

Our measurements are tied to modern morphological sea-level analogs (inner edges of the terraces, maximum retreat points of modern

notches or the limit between vegetation and the highest tide marks, Table 3). Landward, the inner edge corresponds to a break in slope between the terrace surface and the overhanging fossil sea cliff (e.g., Armijo et al., 1996; Jara-Muñoz et al., 2016). When the modern sea-level analogs correspond to high tide marks, we calculate the elevations of the landforms above pmsl, by adding a correction of half the tidal range (Tables 2 and 3).

At Watu Parunu (SE Sumba, Site 1; Fig. 1B; 2; 3) we carried altimetric measurements with a laser distance meter (telemeter Leica Disto 2; ± 1.5 mm in precision). On the West end of Sumba Island (Site 7) and at Cape Laundi (Sites 12 and 13), we obtained topographic profiles of the Holocene coastal terraces using a real-time kinematic differential global positioning system (RTK dGPS) with a vertical accuracy of ~ 8 mm. dGPS elevations are orthometric heights referred to the global geoid
<table><caption>**Table 4**
New <sup>14</sup>C dating of Holocene coastal landform on Sumba Island and associated chemistry.</caption><thead><tr><th rowspan="2">Sample</th><th colspan="2">Sample information</th><th rowspan="2">Sampling information</th><th rowspan="2">Site</th><th rowspan="2">Longitude<br>(E)</th><th rowspan="2">Latitude<br>(N)</th><th rowspan="2">Elevation apmsl<br>(m)</th><th colspan="2">Aragonite</th><th colspan="2">Radiocarbon age</th><th colspan="2"><sup>14</sup>C Chemistry</th></tr><tr><th>Age BP<br>(yr)</th><th>Age BP calibrated<br>(yr)</th><th>Calcite<br>(%)</th><th>Aragonite<br>(%)</th><th>Age BP<br>(yr)</th><th>Age BP calibrated<br>(yr)</th><th>mg C</th><th>Delta C13</th><th>pMC</th><th>Err pMC</th></tr></thead><tbody><tr><td>18.5<br>SL04_07_18</td><td>Tridacna squamosa<br>Diploria spp.</td><td>in situ – reworked<br>in growth position – in situ</td><td>7</td><td>118.9679</td><td>-9.5926</td><td>2.0 ± 0.7</td><td>1.75 ± 0.7</td><td>&lt; 1</td><td>&lt; 99</td><td>1615 ± 30</td><td>1475 ± 70</td><td>1.34</td><td>1.40</td><td>81.79973</td><td>0.23068</td></tr><tr><td></td><td></td><td></td><td>14</td><td>120.2714</td><td>-9.6403</td><td></td><td></td><td>&lt; 1</td><td>&gt; 99</td><td>765 ± 30</td><td>700 ± 30</td><td>1.32</td><td>3.00</td><td>90.92292</td><td>0.21793</td></tr></tbody></table>

model: EGM2008 (Pavlis et al., 2012). At other sites, we repeatedly measured the Holocene inner edge with four barometric altimeters with a 0.5 m precision. As we are studying Holocene terraces, the measurements were taken close to the sea level, making it easy to calibrate the barometric altimeters. The margins of error to our elevation estimates are primarily influenced by factors such as the rugosity of the landforms or the sea-level datums. The combined surface rugosity of the Holocene landforms, deposits and bioconstruction typically falls within the range of 0.5 m in Sumba Island (Chauveau et al., 2021a). The total vertical error is then obtained by adding in quadratic individual errors taking into account the uncertainties from the technique measurement (from 0.08 mm, i.e., dGPS measurement, to 0.5 m, i.e., barometric altimeter), the rugosity (i.e., 0.5 m) and the tide uncertainties (i.e., ~0.08 m; Nienhuis et al., 2020).

To calculate the relative sea-level (RSL) indicators from our elevation measurements, we used IMCalc (Indicative Meaning Calculator, Lorscheid & Rovere, 2019). IMCalc is a Java-app that quantifies the indicative meaning (Table S1) and paleo RSL of sea-level indicators at any given coordinate, if that coordinate falls within the radius of 50 km distance to the closest data point of the Coastal Point Database (CPD) used by Lorscheid & Rovere (2019). IMCalc applies simple hydro- and morphodynamic equations with inputs from global wave (CAWCR, Centre for Australian Weather and Climate Research) and tide (OTPS, OSU (Oregon State University) Tidal Prediction Software) datasets (Table 2). These global datasets of wave and tidal conditions are sampled in a regular distance, which resulted in the CPD and used as the main data input to the IMCalc software (Lorscheid & Rovere, 2019). The dominant wave direction and magnitude significantly influence both shoreline geometry and the ability of coral colonies to flourish (Gischler et al., 2019). As there are no direct measurements of pre-observational wave height, we assume that the modern average wave climate provides an appropriate approximation (Table 2). For further information, please refer to Rovere et al. (2016) and Lorscheid & Rovere (2019). All input and output data are in Tables 2 & S1 (Appendix A. Supplementary data) and in Appendix A. Supplementary data "Supplementary Information IMCalc".

## 3.2. Glacial Isostatic Adjustment

The regional disparities of RSL changes since the Last Glacial Maximum (~20 ka BP) are a result of the combined influences of local Glacial Isostatic Adjustment (GIA), tectonics and other local processes (e.g., Lambeck et al., 2014; Khan et al., 2015). Here, we use the ICE-7G_NA (VM7) model (Roy & Peltier, 2015; 2017; 2018). This model is based upon a detailed analysis of the regional convergence of the iterative procedure that has been used in the generation of global GIA, such as the ICE-6G_C (VM5a) model (a model of the last deglaciation event of the Late Quaternary ice age, Peltier et al., 2015) and its precursors (e.g., see Argus et al., 2014 for a discussion of the Antarctic component of this model). Thus, the ICE-7G_NA (VM7) model succeeds the ICE-6G (VM5a) and the ICE-5G (VM2 L90) models as the most extensively validated combination of ice thickness history (ICE-xG) and radial viscosity profile (VMy) (Roy & Peltier, 2015, 2017, 2018). As the model has a 1x1 degree grid, five cells surround Sumba Island. The RSL curves presented in the manuscript represent the mean of these cells with an uncertainty based on a standard deviation. We also integrate a maximum uplift rate component of 0.65 mm a⁻¹ (calculated at Waingapu, Fig. 1B, Nexer et al., 2015) in the GIA curve in order to obtain a maximum RSL range for the whole island.

## 3.3. AMS<sup>14</sup>C dating and Holocene inference

At Site 7 (in the western part of Sumba, Fig. 1B), we sampled a *Tridacna squamosa* bivalve (sample SUM 18–5) from the lowest sedimentary terrace. At Site 14 (Waingapu, Fig. 1B), we drilled a coral (*Diploria* sp.) near the modern shoreline (below the lowermost CRT). These samples were dated using <sup>14</sup>C accelerator mass spectrometry (Orsay,
<figure><img src="image_9.png" /><figcaption>**Fig. 7.** The coastal record on the NW tip of Sumba sequence. A) Location of the studied area. B) The Mandorak area and location of site 8. C) Aerial interpreted picture of a karst-type coast. D) Interpreted picture of Mandorak (Site 8). Satellite images of A and B are from Google Earth (@Maxar Technologies, @TerraMetrics, @DigitalGlobe, Data SIO, NOAA, U.S. Navy, NGA, GEBCO).</figcaption></figure>

GEOPS, France). The calcite and aragonite contents of the samples were estimated using a XRD Brucker D8 from the CYBER facility ("CYcles Bio-géochimiques Et Ressources" team, Geo-Ocean Laboratory, IFREMER) in Brest (France). The morpho-stratigraphy, i.e., the correlation of coastal terraces, when present, to the Holocene was based on the morphological characteristics of the landforms as well as on the new ¹⁴C ages (Site 7 & 14) and 18 previously dated samples, most of them on Cape Laundi (17 at site 13) and one at Wanokaka (Site 4, Table 1).

# 4. Results

## 4.1. Holocene coastal landforms

We describe the Holocene coastal record at fifteen sites (Fig. 1B; 2).

Seven sites are located on the windward southern coast (Figs. 2–6) and eight sites on the leeward northern coast of the island (Figs. 2; 7–11). To our knowledge, except site 4 (Wanokaka) and sites 12/13 (Cape Laundi), none of these sites has been previously described. The sites are characterized by either the lack (Sites 2, 3, 5, 8, 9) or occurrence (Sites 1, 4, 6, 7, 10, 11, 12, 13, 14, 15) of Holocene coastal landforms. Those, dated or inferred, were mostly represented by sedimentary terraces (Sites 4, 6, 7, 10, 11, 15; Table 2), but also by marine terraces (Site 1) and emergent reefs (Sites 13 and 14) with or without associated clastic conglomerate, and by mangroves associated with ramps and benches (i.e., marine terrace reduced in width) and/or notches (Sites 12 and 15). The Holocene coastal record of Sumba is **1**) variable in terms of landforms, bio-constructions and deposits, **2**) discontinuous, **3**) linked to the upper Pleistocene CRTs when present (erosion, re-occupation, re-shaping), and
<figure><img src="image_10.png" /><figcaption>Fig. 8. The central North coast of Sumba. A) Location of the studied Holocene coastal sites 9, 10 and 11. B) Site 10. C) Site 11. D) Interpreted picture of site 11. Satellite images of A, B, and C are from Google Earth (@Maxar Technologies, @TerraMetrics, @DigitalGlobe, Data SIO, NOAA, U.S. Navy, NGA, GEBCO).</figcaption></figure>

at some places 4) currently eroded by the sea in its distal part or 5) characterized by sedimentation in mangrove sections. In terms of reefal constructions, we observed some continuous and thick reefs with branching corals along the leeward northern coast. Alongshore the windward southern coast, the reef crest is often algal and the reef thinner.

## 4.2. Site descriptions: Windward southern coast

### 4.2.1. Site 1: Watu Parunu

Watu Parunu is located West of the Baing embayment and beach (SE Sumba, Site 1; Fig. 3). At Watu Parunu, an active sea cliff associated with a 350 to 650 m-wide modern rocky-shore platform is carved into the Miocene/Pliocene tuffs and pelagic carbonates of the Kananggar Fm. (Fig. 1B; 3). The inner edge of the platform is colonized by calcifying algae and corals. Immediately West of the beach, the rocky coastline is defined by a ~32 × 7 m promontory, named Watu Parunu (Fig. 3C). The promontory includes multiple sea-arches as well as an isolated marine terrace covered by coastal deposits (Fig. 3D–G). This layer is a raised beach that unconformably rests upon the Kananggar Fm. and is tapped by continental colluvial deposits with debris coming from the same formation (Fig. 3D, E).

The coastal deposits form a < 1 m-thick layer of clastic conglomerates with pebbles and within a poorly consolidated sandy matrix. In the deposits, a fragment of *Porites* sp. was collected but the percentage of

calcite (~84 %) suggest significant recrystallization that preclude ¹⁴C- or U-series dating. To the West of the promontory, the coastal deposits thin up landward and end up on the inner edge of the marine terrace. The Holocene inner edge is located above its modern counterpart, overlying a sea-arch and underlying a steep cliff of soft sediments (Fig. 3G).

Such configuration precludes any direct elevation measurements with dGPS or altimeters, which led us to opt for laser distance meter (telemeter) measurements. We chose the limit between the coastal conglomerate and the marine terrace as the inner edge (Fig. 3G). We performed 25 telemeter measurements which led us to estimate the inner edge of the marine terrace at 4.4 ± 0.5 m above pmsl (Fig. 3G, Table 3).

### 4.2.2. Site 2: Tarimbang embayment

About 70 km west of Watu Parunu, the ~ 2.5 × 2.0 km Tarimbang embayment is bordered by wide rocky-shore platforms, associated with coral-colonies at their distal edges (Site 2; Fig. 1B; 4). On both sides of the embayment, rocky-shore platforms are limited landward by active sea cliffs carved into the Kananggar Fm. soft rocks. There, we observed no Holocene coastal landforms.

### 4.2.3. Sites 3 and 4: Wanokaka embayment

We made observations to the East of Cape Karoka (Fig. 1; 5A): on both sides of Wanokaka embayment (Sites 3 and 4; Fig. 5A, B, E, F, G).
<figure><img src="image_11.png" /><figcaption>**Fig. 9.** The Holocene coastal record on the East flank of Cape Laundi (Sites 12 and 13). A-B) Cartography of emerged coral reef terrace sequence of Cape Laundi (modified from Chauveau et al., 2021a, 2021b, 2024a) and location of sites 12 and 13. Interpreted pictures of C) Site 12 and D) Site 13. E) Aerial view of the low CRTs. Photo C was taken during high tide, and D) and E) between low and high tide. Satellite image of A is from Pleiades satellite imagery (1 m resolution) and B is from Google Earth (@Maxar Technologies, @TerraMetrics, @DigitalGlobe, Data SIO, NOAA, U.S. Navy, NGA, GEBCO).</figcaption></figure>

The ~ 4.8 x 1.3 km Wanokaka embayment (Fig. 5B) is bordered by active sea cliffs and does not exhibit low-standing coastal terraces (Site 3; Fig. 5B, E).

At Waiwuang, West of Wanokaka embayment (Site 4; Fig. 5A, B), we observed a narrow (10–15 m wide) low-standing sedimentary terrace (Site 4; Fig. 1; 5E, F). The coastal terrace includes an emergent reef, currently eroded at sea level (Fig. 5F), covered by a sedimentary layer that forms the main surface of the terrace. The inner edge of the sedimentary terrace reaches an elevation of 4.9 ± 0.5 m above pmsl. The terrace deposits terminate landward at a fossil sea cliff carved into Pleistocene reefal limestone (Authemayou et al., 2022). Sampled within the sandy deposit of the terrace, a gastropod was cross-dated by $^{230}$Th/U and $^{14}$C yielding ages of 145 ± 145 and 3400 ± 520 yr BP, respectively (Table 1, Authemayou et al., 2022). Neither age, however, has been deduced to be more robust than the other. We therefore consider the two ages as the limits of an age range, implying that the sedimentary terrace was formed during the end of the Holocene.

### 4.2.4. Site 5: Wakukaka beach

At Wakukaka pocket beach (Site 5; Fig. 5A, C, D), rocky-shore platforms are limited landward by active sea cliffs carved into the Kananggar Fm. soft rocks. There, we did not observe any Holocene coastal landform.

### 4.2.5. Sites 6 and 7: Kodi

On the western part of the island, around Kodi village (Sites 6 & 7; Fig. 1B; 6B), we observed a low-standing sedimentary terrace. At site 7, the sedimentary deposits of the terrace are overlying reefal limestone.

NW of Kodi village (Site 7), the coastal terrace is 200 ± 50 m wide and has its inner edge at 5.1 ± 0.7 m above pmsl. The terrace is heavily reworked (Fig. 6C, D). From this site, a *Tridacna squamosa* shell yielded a calibrated $^{14}$C age of 1475 ± 70 yr BP (18–5, Table 4).

## 4.3. Site descriptions: Leeward northern coast

### 4.3.1. Site 8: Mandorak

To the NW tip of the island, the coastline is indented, karstified and consists of sea cliffs carved into the epi-karstified reefal limestone forming the Pleistocene CRT sequence (Site 8; Fig. 1B; 7). Generally, this coastal stretch does not exhibit a modern fringing reef (Fig. 7B, C). North of Mandorak village, we observed a ~ 10 m high plunging sea cliff exhibiting recrystallised corals (Fig. 7B), but there is no Holocene coastal terrace.

### 4.3.2. Site 9: Tambolaka

To the NE of Tambolaka city (Site 9; Fig. 1B; 8A) the coastline includes a modern beach connected, without a clear marked sea-cliff, to a
<figure><img src="image_12.png" /><figcaption>**Fig. 10.** The Holocene coastal record east of Waingapu city (Site 14) North of Sumba Island. A-B) Location of the studied Holocene coastal site 14. C-D) Interpreted picture of site 14. E) SI_04_07_18 sample (Diploria spp.). Satellite images of A and B are from Google Earth (@Maxar Technologies, @TerraMetrics, @DigitalGlobe, Data SIO, NOAA, U.S. Navy, NGA, GEBCO).</figcaption></figure>

wide, most probably compound CRT (de Gelder et al., 2023). The CRT includes on its surface red-clays resulting from continental alteration and most probably testifying for the antiqueness of the CRT. No well-defined landform can readily be interpreted as Holocene low-standing coastal terrace above sea level.

### 4.3.3. Sites 10 and 11: Cape Mamboro and Cape Sasar

At Cape Mamboro (Site 10; Fig. 1B; 8B, C) and Cape Sasar (Site 11; Fig. 1B; 8D), low-standing coastal terraces are irregularly present at the base of the Pleistocene CRT sequences. To the W of Cape Mamboro (Site 10; Fig. 8A, B, C), the Holocene coastal terrace is sedimentary and ~50 m to ~100 m wide. We did not observe emergent reefal limestone below the terrace clastic deposits. We measured the elevation of the Holocene terrace inner edge at 3.9 ± 0.7 m above pmsl (Fig. 8B). Holocene sedimentary terraces also extend on the western and eastern side of Cape Sasar (Fig. 8A, D). To the West of the Cape (Site 11; Fig. 1B; 8A, D), we measured the inner edge of a sedimentary terrace at 6.9 ± 0.7 m above pmsl (Fig. 8D).

### 4.3.4. Sites 12 and 13: Cape Laundi

On the North-eastern side of Cape Laundi (Fig. 9A), at site 12 (Fig. 9B), an emergent reef forms a narrow (~5 m wide) terrace limited by a ~3 m high fossil sea cliff. The base of the terrace is carved by the modern high tide notch (Fig. 9C). The fossil shoreline includes a fossil sea-cave of a few metres deep carved into the CRT limestone (Fig. 9C).

Numerous present-day analogues to this cave are visible alongshore Cape Laundi. The inferred Holocene inner edge is at 3.5 ± 0.5 m above pmsl (Fig. 9C).

Southward of site 12, at site 13, we observed remnants of an emergent reef at 1.1 ± 0.5 above pmsl (Jouannic et al., 1988; Pirazzoli et al., 1991, 1993; Bard et al., 1996; Chauveau et al., 2021a). The 17 samples dated at Cap Laundi come from this Holocene feature or nearby (Table 1, Fig. 9D). In this area, the inner edge of the Holocene coastal terrace has been erased, and forms a compound terrace with the first Pleistocene CRT (i.e., CRT $I_1$, inner edge measured at 6.4 ± 0.5 m above pmsl by Chauveau et al., 2021a; Fig. 9E).

### 4.3.5. Site 14: Waingapu

Waingapu city is mainly built on an emerged sequence of CRTs, which define a small cape, between two streams flowing out into Waingapu Bay (Fig. 1B; 10A). East of Waingapu city (Site 14; Fig. 1B; 10A, 10B), the modern coastline is characterized by a fringing coral reef and mangrove trees. Coastal sediments are associated with a rocky-shore platform including a “ramp” and carved into older Pleistocene reefal limestone (Fig. 10C). The rocky-shore platform is sometimes limited landward by a low sea cliff (< 1.5 m), associated with a flat surface that is reduced in width and which we interpret as a narrow CRT (Fig. 10C, D). The inner edge of this reduced CRT was measured at 2.9 ± 0.5 m above pmsl. *Diploria* sp. coral sampled just below the modern inner edge yielded an age of 700 ± 30 yr BP (Table 4; Fig. 10D, E).
<figure><img src="image_13.png" /><figcaption>**Fig. 11.** The Holocene coastal record north of Cape Undu (Site 15), NE Sumba. A) Location of the studied Holocene coastal site 15. B-C) Location of site 15. D) Picture showing the site at low tide. Satellite images of A, B and C are from Google Earth (@Maxar Technologies, @TerraMetrics, @DigitalGlobe, Data SIO, NOAA, U. S. Navy, NGA, GEBCO).</figcaption></figure>

### 4.3.6. Site 15: North of Cape Undu

On the NE tip of the Island (north of Cape Undu, Site 15; Fig. 1B; 11) we observed a similar environment to that of site 14, but with more coastal sediments and more developed mangroves. Site 15 is located on the NW tip of a rather wide and continuous sedimentary Holocene terrace (Fig. 11B). To the NW the sedimentary terrace is replaced by mangroves. We observed an inactive notch located at 2.4 ± 0.7 m above pmsl, the base of which is rarely reached by high tides (Fig. 11). We consider that it probably corresponds to the inner edge of the Holocene sedimentary terrace.

## 5. Discussion

The assessment of preserved and absent Holocene coastal archives around Sumba Island allows us to discuss their morphological differences, their preservation, as well as to extract a relative sea-level history.

### 5.1. Elevations of Holocene inner edges

The inner edges measured around Sumba do not appear to be directly related to uplift rates (Fig. 12A). The Holocene inner edge at site 14 (Waingapu) is one of the lowest (i.e., 2.9 ± 0.5 m above pmsl), while the area is affected by the highest rate of uplift on the island (0.60 ± 0.5 mm a⁻¹, Fig. 12A). In contrast, the Holocene inner edge at site 11 (West Sasar) is the highest measured (i.e., 6.9 ± 0.7 m above pmsl), despite one of the lowest uplift rates (0.26 ± 0.5 mm a⁻¹, Fig. 12A). An inverse linear relationship is even possibly observed, i.e., the higher the uplift rate, the lower the inner edge (Fig. 12A). Conversely, it seems that the

higher the wave height, the higher the inner edge (Fig. 12B). The sites on the windward southern coast (Sites 1, 4 and 7), which are affected by higher wave heights (mean and maximum) than those on the leeward northern coast (Table 2; Fig. 12B), have higher inner edges than their leeward counterparts (with the exception of Site 11). However, the correlations calculated from the relationships between the inner edge elevations and the uplift rate (R² = 0.34, n = 9, Fig. 12A), mean (R² = 0.17, n = 9, Fig. 12B) and maximum (R² = 0.30, n = 9, Fig. 12B) wave height remain low and not significant. In addition, we did not notice any significant difference between the elevation of the sedimentary (5.2 ± 1.6 m above pmsl, n = 5) and marine (3.6 ± 0.7 m above pmsl, n = 3) terraces (Table 3, Fig. 12).

As their Pleistocene counterpart, the Holocene coastal record may be influenced by the morphology of antecedent terraces (Maxwell et al., 2025). For example, it would be much easier to deposit Holocene corals on a flat Pleistocene terrace that is a few meters deep (leeward northern coast, e.g., Site 12), than against a steep cliff without such a convenient starting point (windward southern coast, e.g., Site 5). The antecedent topography will therefore have a direct role on the reef construction and/or the sediment deposition in the first place, but also on its extension towards the ocean and its elevation relative to the pmsl.

Reef growth varies regionally, by a factor of 3 to 6 between Tambolaka (West Sumba, reef growth rate < 4 mm a⁻¹) and Cape Laundi (East Sumba, reef growth rate > 6 mm a⁻¹, de Gelder et al., 2023). Moreover, the Holocene/present-day reef platform is submerged at Tambolaka but is exposed at Cape Laundi (de Gelder et al., 2023). In addition to regional uplift rate discrepancies, differences in reef growth rates directly influence the thickness of the reef built and therefore
<figure><img src="image_14.png" /><figcaption>**Fig. 12.** Elevation of the Holocene inner edges in Sumba Island in relation to A) the uplift rates and B) the wave height (Hs) from the Centre for Australian Weather and Climate Research (CAWCR) global hindcast raster (Table 2). The grey zone in A) corresponds to the theoretical elevation of inner edges 6 ka ago, taking into account the GIA (ICE-7G_NA, i.e., 1.2 m), all as a function of uplift rate. This grey zone therefore corresponds to the theoretical maximum elevation of Holocene landforms. This shows that the inner edges of sites 1, 4, 7, 10 and 11 have a higher elevation than the calculated theoretical value.</figcaption></figure>

indirectly have an impact on the elevation of the CRT inner edge.

Finally, Holocene inner edge elevations are inherently complex, given the simultaneous contribution of all processes involved in their morphogenesis: sea-level variations, uplift rates, wave heights, type of terrace, antecedent morphology, reef growth rates, erosion (marine and continental), and sediment deposition rates. For instance, in Sumba Island, spatial differences in uplift rates are expected to manifest as variations in the inner edge elevations of Holocene coastal landforms, with higher uplift rates yielding higher elevations. Yet, this pattern is not observed. Thus, in Sumba Island, as everywhere else, each process of morphogenesis must be carefully evaluated—and quantified when possible—before attributing causality to any one of them.

## 5.2. Preservation of the Holocene landforms

Exposure to prevailing winds typically imprints a distinctive hydrological, erosional, and biological asymmetry to island topography and their coastal regions. Such a windward/leeward asymmetry has been observed for volcanic islands (Ramalho et al., 2013) and islands exhibiting sequences of CRTs (e.g., Muhs et al., 2012; Speed and Cheng, 2021). Alongshore Sumba, Holocene terraces are preferentially preserved on the leeward northern coast of the island (North coast, e.g., Effendi and Apandi, 1993). However, these terraces are discontinuous over tens of kilometres (e.g., Sites 8, 9), unlike the older Pleistocene coastal terraces (Fig. 7). As a result, subaerial Holocene terraces rarely form better preserved mirror images of the Pleistocene counterpart. For example, at Cape Sasar, Holocene coastal terraces are preserved on

concave segments of coast (embayment) whereas Pleistocene terraces are laterally continuous around the cape (Fig. 8C, D). On the windward southern coast, Holocene (as Pleistocene) coastal landforms, deposits and/or bioconstructions are found sporadically, as relicts, in rather protected areas when carved into the soft rocks of the Kananggar Fm. (e. g., Site 1, Fig. 3) or associated with CRT sequences (e.g., Sites 4, 6, 7; Fig. 5; 6). The modern shoreline, mostly carved into the Kananggar Fm., is also much more indented on the windward southern coast. It exhibits a higher degree of fractalization, with intricate capes and embayment at different scales (Fig. 1; 3A, B, C; 4A, B, C).

Emerged coastal terraces are eroded during sea-level regression, leading to the partial dismantling of reef and/or sedimentary units (Chauveau et al., 2024a). The RSL regression since 6 ka (Fig. 13) may therefore be partly responsible for the formation of two distinct Holocene units (one emerged and one corresponding to the current platform), thus breaking a continuous Holocene record around Sumba. Also, the greater the bedrock slope, the more easily and quickly the emerged coastal features will be eroded (Chauveau et al., 2024b). In addition to lower reef growth rates, softer and more steeply sloping substrate, the higher wave energy would explain the rarity of Holocene formations on the windward southern coast. The same applies to the sequence of terraces observed sporadically and only in the bays to the south of the island (Site 4, Authemayou et al., 2022). This difference in preservation will increase as a result of the current rise in sea level (Fox-Kemper et al., 2021), which will lead to an irremediable loss of Holocene coastal landforms (e.g., the eroded sedimentary terrace at Waiwuang, Fig. 5F, or the collapsed blocks in Cape Laundi, Fig. 9C). Ultimately, this study
<figure><img src="image_15.png" /><figcaption>**Fig. 13.** Holocene relative sea level in Sumba Island. The elevation of site 13 was remeasured and homogenized at $1.1 \pm 0.5$ m above pmsl. The green and purple RSL curves are the average of the five ICE-7G_NA (VM7) cells surrounding Sumba Island (Roy & Peltier, 2015; 2017; 2018), with uncertainty based on a standard deviation, without and with the maximum uplift rate integrated (calculated at Waingapu, Fig. 1B, Nexer et al., 2015). Samples 18–5 (Site 7) and SI_04_07_18 (Site 14) are the samples dated in this study (Table 4). As samples 18–5 & 18–12B have been reworked, we consider the inner edge elevation to be representative of these SLIPs. We also take the inner edge of the Holocene CRT of site 14 as a SLIP. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

contributes to the archiving of fossil coastal records threatened by the intensifying impacts of climate change.

### 5.3. Relative sea level

The spatio-temporal framework (provided by the previous studies and this one) allow the calculation of SLIPs for the whole island of Sumba (Fig. 13). These index points come from five sites and are calculated from inner edges (Sites 4, 7 & 14), a high tide notch (Site 12) and *in situ* corals (Sites 13 & 14).

Our calculated SLIPs are relatively in good agreement with GIA curves (without and with integrated uplift rate, green and purple curves in Fig. 13, respectively). A first group of corals (Site 13) and the high tide notch (Site 12) forms from 6500 to 4870 yr BP. A second group stands out from 2540 (Site 13) to 1405 yr BP (Site 7). Both groups appear to be at the same RSL (from 1.84 to at least 4.5 m above pmsl, Fig. 13). The SLIPs inferred from the second group (from 2540 to 1405 yr BP) are, however, slightly above the predictions of the GIA curves (Fig. 13). Concerning the *in situ* corals of Site 13, this abnormally high calculated RSL can be explained by the growth of corals in high tide pools present on the older Holocene unit (that of the first group aged from 6500 to 4870 yr BP; Chauveau et al., 2021a). Finally, this study provides new RSL data that enhance and expand the regional record for Southeast Asia and the eastern Indian Ocean (e.g., Mann et al., 2016; 2019; Bender et al., 2020; Ranasinghe et al., 2025).

### 5.4. Future investigations

We present a precise morphological description with a review of the dating and altimetry data for each of the different sites as well as their transcription into SLIPs. This study can therefore serve as a basis for future investigations. For example, more fossil corals of Holocene age could be sampled and dated at site 14 (Waingapu; Fig. 2). Better defining the variability of the RSL around the island of Sumba would contribute to global knowledge of past sea-level fluctuations, as well as quantifying

the relative influence of the processes involved in the morphogenesis of Holocene coastal landforms.

## 6. Conclusions

We investigated the Holocene coastal terraces of Sumba Island and described fifteen sites: seven on the windward (South) and eight on the leeward (North) coasts of the island. The sites are characterized by either the absence or presence of low-standing Holocene coastal landforms. The correlation of the coastal terraces to the Holocene is based on the morphological characteristics of the landforms as well as $^{14}$C and U/Th ages. The Holocene coastal landforms are represented by a variety of facies of sedimentary and marine terraces, sometimes carved into emergent reefs and/or associated with clastic conglomerate. The elevation of the inner edges of Holocene coastal terraces are ranging from $2.4 \pm 0.7$ m to $6.9 \pm 0.7$ m above the present mean sea level, reflecting the interaction between glacio-eustatism, land motion, and local hydrodynamics, but their relative influence remains indivisible with current data. However, independently derived paleo sea-level indicators from Holocene leeward and windward morphologies may yield divergent relative sea-level histories. Thus, coastal terrace derived paleo sea-level index point accuracy is directly contingent upon the inclusion of localized geodynamic, hydrodynamic, and morphodynamic processes governing shore morphogenesis. Finally, we highlight the sites that have the greatest potential for more detailed investigations on local Holocene formations and relative sea-level reconstructions.

### CRediT authorship contribution statement

**Denovan Chauveau:** Writing – original draft, Validation, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. **Kevin Pedoja:** Writing – original draft, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Christine Authemayou:** Writing – review & editing, Validation, Supervision, Methodology, Investigation,
Funding acquisition, Conceptualization. **Laurent Husson:** Writing – review & editing, Validation, Investigation, Funding acquisition, Formal analysis, Conceptualization. **Gino de Gelder:** Investigation, Writing – review & editing, Validation, **Sonny Aribowo:** Writing – review & editing, Validation, **Anne-Morwenn Pastier:** Writing – review & editing, Validation, **Danny Hilman Natawidjaja:** Writing – review & editing, Investigation. **Vera Christanti Agusta:** Writing – review & editing, Investigation, **Sri Yudawati Cahyarini:** Writing – review & editing, Investigation, Funding acquisition, Formal analysis, Conceptualization.

## Funding

This work is part of the PLOMA project (led by Denovan Chauveau) which is supported by ISblue project, Interdisciplinary graduate school for the blue planet (ANR-17-EURE-0015) and co-funded by a grant from the French government under the program "Investissements d'Avenir" embedded in France 2030. This work was supported by public funds received from the program "Investissements d'Avenir" managed by the French National Research Agency (ANR-10-EQPX-20 and ANR-10-LABX-19-01, Labex Mer, CLIMORESO, Christine Authemayou), the INSU Tellus Syster program (SECOMAS, Christine Authemayou), and the CNES TOSCA program (CETTROPICO, Christine Authemayou). We thank the National Geographic Explorer grant (no CP 087R 17) to support the Indonesian researchers (Sri Yudawati Cahyarini, Vera Christanti Agusta and Danny Hilman Natawidjaja).

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgments

We thank the State Ministry of Research and Technology of Indonesia "RISTEK" that allowed us to conduct the field trip to Sumba (research permit 680/FRP/E5/Dit.KI/IV/2017). In this work, we use the global wave hindcast data from the Centre for Australian Weather and Climate Research (CAWCR), a partnership between the Bureau of Meteorology and CSIRO. Hindcast modelling undertaken as part of the PACCSAP (Pacific-Australia Climate Change Science and Adaptation Planning) Project 4.3 "High resolution wind-wave climate and projections of change in the Pacific region for coastal hazard assessments" in 2012, and extended with support from COSPPAC (Climate and Oceans Support Program in the Pacific). This project was funded by DCCEE and AusAID and undertaken jointly by CSIRO and the BoM. Model run on the Bureau of Meteorology SOLAR facility and NGAMAI facility. We thank the editor and the two anonymous reviewers for their constructive and prompt comments and suggestions.

## Appendix A. Supplementary material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jaesx.2025.100208.

## Data availability

The initial dataset (dating and topographic measurements) is provided in the main manuscript (Tables 1, 2, 3, and 4). Appendix A. Supplementary data contains Tables S1 and S2. Table S1 show the list of sea-level indicators and their indicative meaning. Table S2 contains the location of sites where no Holocene features were observed. All input and output data used with IMCalc can be found in

"Supplementary Information IMCalc".

Data will be made available on request.

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