Sustained coral reef growth in the critical wave dissipation zone of a Maldivian atoll

Sea-level rise is expected to outpace the capacity of coral reefs to grow and maintain their wave protection function, exacerbating coastal flooding and erosion of adjacent shorelines and threatening coastal communities. Here we present a new method that yields highly-resolved direct measurements of contemporary reef accretion on a Maldivian atoll reef rim, the critical zone that induces wave breaking. Results incorporate the suite of physical and ecological processes that contribute to reef accumulation and show growth rates vary from 6.6 ± 12.5 mm.y−1 on the reef crest, and up to 3.1 ± 10.2 mm.y−1, and −0.5 ± 1.8 mm.yr−1 on the outer and central reef flat respectively. If these short-term results are maintained over decades, the reef crest could keep pace with current sea-level rise. Findings highlight the need to resolve contemporary reef accretion at the critical wave dissipation zone to improve predictions of future reef growth, and re-evaluate exposure of adjacent shorelines to coastal hazards.

FACIES DISTRIBUTION OF KAIS FORMATION IN “X” FIELD, SALAWATI BASIN, WEST PAPUA, INDONESIA

<p class="Abstract">Daerah penelitian lapangan “X” terletak di Formasi Kais, Cekungan Salawati, Papua Barat, Indonesia. Maksud dan tujuan dari penelitian ini adalah untuk menginterpretasikan fasies karbonat, beserta penyebarannya, baik secara vertikal maupun horizontal. Penelitian dimulai dengan penafsiran <em>litostratigrafi</em> menggunakan data <em>log</em> dan sayatan tipis, untuk membuat <em>type log</em>. Dilanjut dengan analisis sikuen stratigrafi dan <em>reef system</em> untuk menentukan penyebaran, dengan bantuan data seismik untuk dikorelasikan dengan sumur-sumur lainnya. Dari hasil analisis, terdapat 5 fasies pada daerah penelitian, yaitu: <em>Skeletal Debris Packstone-Wackestone, Coral Algal Grainstone – Boundstone, Skeletal Wackestone, Skeletal Packstone dan Coral Algal Packstone</em>. Terdapat pula 4 <em>reef system</em>, yaitu; <em>Back reef, reef crest, fore reef dan off reef</em>. Untuk mencapai tujuan akhir dari penelitian ini, maka dibuat peta penyebaran fasies.</p>

Influence of reef flat submergence on infra-gravity wave energy and resonance over the fringing reef

Fringing reefs which are common nearshore islands with coral reef growth have special topography of very steep slope on the fore-reef and mild slope on the wide flat. When incident waves propagate from a very deep water region (from hundreds of meters to thousands of meters of depth) to approaching the reef they abruptly commence a very shallow water (only few centimeters to several meters of depth) and create strong hydrodynamic processes on the reef flat. Due to shallow depth, waves feel the bottom and break in the area of fore-reef slope and reef crest and partial reef flat. Infra-gravity waves (IG), other name as bound long waves or surf beat, which belong to low-frequency wave type (0.002Hz ¸ 0.04Hz) are generated by the varying-breaking point mechanism on the shallow reef flat. On the flat, short wave energy is almost dissipated; low-frequency waves are strongly dominated over the surf zone till swash zone. Wave set-up causing an increase of water level on the flat combines with the run-up at the shoreline which can lead to coastal flooding. Besides, if the reef flat length is in the order of one fourth of wavelength the first oscillation resonant mode with standing wave occurs. This component is resonantly amplified at the shoreline relative to the incident infra-gravity wave energy at the reef crest.

Light Limitation and Depth-Variable Sedimentation Drives Vertical Reef Compression on Turbid Coral Reefs

Turbid coral reefs experience high suspended sediment loads and low-light conditions that vertically compress the maximum depth of reef growth. Although vertical reef compression is hypothesized to further decrease available coral habitat as environmental conditions on reefs change, its causative processes have not been fully quantified. Here, we present a high-resolution time series of environmental parameters known to influence coral depth distribution (light, turbidity, sedimentation, currents) within reef crest (2–3 m) and reef slope (7 m) habitats on two turbid reefs in Singapore. Light levels on reef crests were low [mean daily light integral (DLI): 13.9 ± 5.6 and 6.4 ± 3.0 mol photons m–2 day–1 at Kusu and Hantu, respectively], and light differences between reefs were driven by a 2-fold increase in turbidity at Hantu (typically 10–50 mg l–1), despite its similar distance offshore. Light attenuation was rapid (KdPAR: 0.49–0.57 m–1) resulting in a shallow euphotic depth of &lt;11 m, and daily fluctuations of up to 8 m. Remote sensing indicates a regional west-to-east gradient in light availability and turbidity across southern Singapore attributed to spatial variability in suspended sediment, chlorophyll-a and colored dissolved organic matter. Net sediment accumulation rates were ∼5% of gross rates on reefs (9.8–22.9 mg cm–2 day–1) due to the resuspension of sediment by tidal currents, which contribute to the ecological stability of reef crest coral communities. Lower current velocities on the reef slope deposit ∼4 kg m2 more silt annually, and result in high soft-sediment benthic cover. Our findings confirm that vertical reef compression is driven from the bottom-up, as the photic zone contracts and fine silt accumulates at depth, reducing available habitat for coral growth. Assuming no further declines in water quality, future sea level rise could decrease the depth distribution of these turbid reefs by a further 8–12%. This highlights the vulnerability of deeper coral communities on turbid reefs to the combined effects of both local anthropogenic inputs and climate-related impacts.

Reef geomorphology and associated habitats of Karimunjawa Islands, Indonesia: a spatial approach to improve coastal and small islands management

The Karimunjawa Islands are situated in the offshore Jepara region of Central Java with abundant coastal and marine resources including coral reefs. The reef geomorphology appears typical of fringing reefs worldwide comprising reef flat, reef crest and reef slope. The reef geomorphic profiles are generally gently sloping seaward with slightly raised reef crest along the reef edge. The reefs slope moderately (15-30°) at the upper forereef slope (~ 5-10 m deep) and tend to drop steeply, sometimes almost vertical, at depths of 10-30 m. The coral communities are found from the intertidal to a depth of about 15 m, with the most vigorous development occurring between 1.5 to 5 m. The reef flats have a low coral cover and are extensively covered by a mixture of seagrass beds and carbonate sand. The reef crests, which mark boundaries between reef flat and upper forereef slope, are mainly colonized by mixed Acropora corals, mainly A. Hyacinthus. The forereef slopes have substantial coral growth prevailing mixed branching Acropora, Porites cylindrica and Porites sp. Sediments on the reef flats are mainly bioclastic materials derived from reef-erosion, including coral fragments, mollusks, foraminifera, red algae, Halimeda, Echinodermata, aggregate, quartz and lithic fragments. Seagrass beds, mainly Enhalus, occur on the inner reef flat and are gradually shifted to macroalgae, predominantly Sargassum. The study provides a basic requirement for fisheries management and environmental monitoring for a mid-Sunda Shelf within a biodiversity “hotspot”.

DENSITAS ZOOXANTHELLAE KARANG FOLIOSE PADA KEDALAMAN BERBEDA (ZONA TERUMBU KARANG) DI PERAIRAN WAWORAHA KECAMATAN SOROPIA

Zooxanthellae merupakan mikroalga yang berperan penting bagi pertumbuhan karang. Penelitian ini bertujuan untuk mengetahui densitas zooxanthellae karang foliose pada 3 zona terumbu karang yang berbeda (reef flat, reef crest, reef slope) di Perairan Waworaha kecamatan soropia, Konawe. Pengambilan data telah dilakukan pada April sampai Mei 2017 melalui dua tahapan yaitu pengambilan sampel jaringan karang foliose di perairan dan perhitungan zooxanthellae di laboratorium.. Pengambilan sampel karang foliose dilakukan dengan metode koleksi bebas (free handpicking) dengan mengunakan alat SCUBA sedangkan analisisi densitas zooxanthellae dilakukan dengan metode homogenisasi. Hasil penelitian menunjukan bahwa densitas zooxanthellae karang foliose di lokasi penelitian rata-rata sebesar 5.1x 106 sel/cm2. Densitas zooxanthellae berdasarkan zona terumbu karang di Perairan Waworaha tercatat paling tinggi pada zona reef flat (7.7 x 106 sel/cm2) diikuti zona reef crest (4.5 x 106 sel/cm2) dan yang terendah berada pada zona reef slope (3.2 x 106 sel/cm2). Perbedaan densitas zooxanthellae pada karang foliose lebih dipengaruhi oleh perbedaan intensitas cahaya.Kata kunci : Densitas zooxanthellae, karang foliose, Perairan Waworaha, zona terumbu karang

Karakteristik Reservoir Berdasarkan Analisis Petrofisik Pada Formasi Baturaja, Lapangan Aulia, Cekungan Jawa Barat Utara

Formasi Baturaja merupakan salah satu formasi penghasil minyak dari Cekungan Jawa Barat Utara. Formasi Baturaja pada Cekungan Jawa Barat Utara ini memiliki keunikan yaitu kondisi batuan yang tergolong tight, namun bisa memproduksi minyak. Lokasi penelitian berada di Lapangan Aulia, Subcekungan Jatibarang. Penelitian ini bertujuan untuk mengetahui variasi litologi secara vertikal, mengetahui lingkungan pengendapan Formasi Baturaja, mendapatkan nilai properti petrofisik dan menentukan kedalaman reservoir yang prospektif.Metode deterministik digunakan dengan pertimbangan lebih cocok pada litologi yang homogen. Data yang digunakan dalam penelitian adalah data dari 6 sumur pemboran. Hasil analisis kualitatif pada semua sumur menunjukkan variasi litologi tersusun dari batugamping dan batugamping sisipan batulempung. Fasies batuan yang terdapat pada Formasi Baturaja berupa packstone dan perselingan packstone – wakckestone hasil pengendapan laut dangkal dengan fasies karbonat yaitu reef crest. Nilai properti petrofisik di Lapangan Aulia memiliki volume shale rata-rata 0,24281 dan nilai rata-rata porositas efektif sebesar 1-6,5% (porositas buruk). Porositas yang rendah pada batugamping Formasi Baturaja ini diinterpretasikan sebagai dampak dari fluktuasi muka laut dan akibat diagenesis batugamping. Nilai permeabilitas rata-rata adalah 0,0134 – 2,0452 mD (tight). Lapisan batuan prospek rerata di Lapangan Aulia adalah 5,67 m dengan lapisan paling tebal dijumpai pada RUO 25, yaitu setebal 9 m di kedalaman 1.846,110 m (TVDSS).

Observing Sea Spray Aerosol Production in the Surf Zone of Hawaii

&lt;p&gt;Sea spray aerosol (SSA) play a significant role in the local climatology of coastal areas through direct radiative forcing and the indirect aerosol effect. Quantifying the size and concentrations of SSA is essential to understanding their influence in these coastal regions. Current observations of SSA in the surf zone come from coastline station measurements. These stations are often limited to observing only the mass of SSA produced and are unable to differentiate SSA concentrations of varying sizes. NCAR has developed an instrument known as a giant nucleus impactor (GNI) that allows deliquesced salt particles to impact onto polycarbonate slides exposed to a free airstream. These slides are then analyzed in a humidified environment under a microscope providing information about the SSA sizes and concentrations present. By modifying the NCAR GNI, we created a smaller, low-cost method known as a mini-GNI from 3D printing and Arduino microcontrollers. Using this new instrumentation, we attached the mini-GNI to a drone that sampled four locations over the ocean perpendicular to the coastline: the outer reef crest, inner reef crest, lagoon area, and shoreline. While sampling occurred, atmospheric and oceanographic measurements were recorded. This methodology provided us a baseline concentration or &amp;#8220;open-ocean&amp;#8221; concentration at the outer reef crest. It allowed us to compare how sizes and concentrations changed as the air parcel interacted with the surf zone. As the sampling locations moved closer to the shore, we&amp;#8217;ve observed an increase in larger and more concentrated SSA that were contributed by the surf zone. We&amp;#8217;ve also found that SSA concentrations have a stronger relationship to wave activity than to wind speed in our coastal environment. The ultimate goal is to quantify how the ocean environment and atmospheric conditions contribute to SSA production in the surf zone.&lt;/p&gt;