Fitria Ratna Pratiwi, Suwarno Hadisusanto, Luli Gustiantini, Nazar Nurdin, Mira Yosi


Laut Halmahera terletak pada Western Pacific Warm Pool (WPWP), yaitu pusat konveksi panas di Samudera Pasifik Barat tropis. Laut ini merupakan salah satu jalur masuk Arlindo yang menghubungkan massa air Samudera Pasifik dengan Samudera Hindia. Sehingga area ini penting untuk rekonstruksi paleoklimat. Peristiwa perubahan glasial akhir-interglasial (Holosen) merupakan peristiwa di masa lalu yang sangat mempengaruhi kondisi Laut Halmahera. Salah satu proksi yang dapat digunakan untuk mencatat perubahan iklim di masa lalu adalah sisa-sisa makhluk hidup, termasuk foraminifera. Perubahan yang terjadi pada foraminifera dapat diamati dari tingkat  keanekaragaman, kemelimpahan, dominansi, dan keseragaman. Penelitian dilakukan dengan menggunakan sampel sedimen bor MD10-3339, yang diambil di Laut Halmahera (00o26,67’LS dan 128o50,33’BT) pada kedalaman 1.919 m, dalam survei MONOCIR 2 tahun 2010. Sampel yang digunakan pada rentang 20 cm hingga 1.930 cm dengan interval 60 cm pada tiap sampel, yang dianggap mewakili waktu terjadinya glasial-interglasial. 30 sampel kemudian diamati dan dilakukan analisis secara kuantitatif. Teridentifikasi 52 spesies yang terdiri dari 32 spesies foraminifera bentonik dan 21 spesies foraminifera planktonik. Nilai indeks keanekaragaman, nilai indeks keseragaman, dan indeks dominansi menunjukkan nilai yang fluktuatif sejak glasial-interglasial, dengan nilai rata-rata 1,66; 0,35; dan 0,3. Walaupun tidak menunjukkan pola glasial-interglasial, namun pada sekitar umur 12.519 BP, nilai indeks keanekaragaman dan nilai keseragaman menunjukkan nilai yang lebih rendah dibandingkan dengan nilai yang lain yaitu 1,102 dan 0,26. Sebaliknya, indeks dominansi mencapai nilai tertinggi yaitu 0,55.  Selain itu, persentase P. obliqueloculata pada umur ini menjadi sangat dominan yaitu 73,05%. Hal tersebut kemungkinan berkaitan dengan peristiwa Younger Dryas.

Kata Kunci : Foraminifera, Younger Dryas, Laut Halmahera.

Halmahera Sea lies in the centre of Western Pacific Warm Pool (WPWP), the warmest area in Tropical Pacific Ocean that play a role as center of heat convection. It is also one of the Indonesian throughflow pathways connecting water mass from Pacific Ocean to The Indian Ocean, therefore this area is considered important for climatic reconstruction. Glacial-interglacial cycle is one of the major events in the past that strongly influence the Halmahera Sea. Potential proxies for paleoclimatic reconstruction are including living organisms remain, such as foraminifera. Respond of foraminifera can be observed from their diversity, abundance, dominance, and their evenness. This study was conducted by analizing sediment core MD10-3339, collected from the Halmahera Sea (00o26.67” S, 128o50.33” E) in 1,919 m water depth, during the cruise MONOCIR 2 in 2010. Samples were analized from 20 cm to 1,930 cm at 60 cm intervals. A total of 30 samples were observed and analyzed. 52 species of foraminifera are found, composed of 32 species of benthonic foraminifera and 21 species of planktonic foraminifera. The analyses of diversity index, evenness, and dominance indicate fluctuated values between glacial-interglacial, with averages values are 1.66, 0.35, and 0.3 respectively. Although the values do not indicate glacial-interglacial trend, however, in 12,519 BP diversity index and evenness index showed the lowest number compared to the other ages (1.102 and 0.26, respectively),in contrast the highest dominance index (0.55). Furthermore, at this time, the percentage of Pulleniatina obliquiloculataincrease (73.05%) and become dominant. This occurrence might be related to the Younger Dryas event.

Keywords: Foraminifera, Younger Dryas, Halmahera Sea.


Foraminifera; Younger Dryas; Laut Halmahera

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