Sedimentary supply of humic-like fluorescent dissolved organic matter and its implication for chemoautotrophic microbial activity in the Izu-Ogasawara Trench

Microbial community structure in the hadal water is reported to be different from that in the upper abyssal water. However, the mechanism governing the difference has not been fully understood. In this study, we investigate the vertical distributions of humic-like fluorescent dissolved organic matter (FDOMH), chemoautotrophic production, apparent oxygen utilization (AOU), and N* in the Izu-Ogasawara Trench. In the upper abyssal waters (< 6000 m), FDOMH has a significantly positive correlation with AOU; FDOMH deviates from the relationship and increases with depth without involving the increment of AOU in the hadal waters. This suggests that FDOMH is transferred from the sediments to the hadal waters through pore water, while the FDOMH is produced in situ in the upper abyssal waters. Chemoautotrophic production and N* increases and decreases with depth in the hadal waters, respectively. This corroborates the effluxes of dissolved substances, including dissolved organic matter and electron donors from sediments, which fuels the heterotrophic/chemoautotrophic microbial communities in the hadal waters. A simple box model analysis reveals that the funnel-like trench topography facilitates the increase in dissolved substances with depth in the hadal waters, which might contribute to the unique microbiological community structure in these waters.

A New Estimate of Global Ocean Climatology

&lt;p&gt;The estimation of climatology is a key element for improving our understanding of the ocean state. Historical data sets available today enables an almost complete reconstruction of global ocean fields. In this study, a new global ocean climatological estimate of basic physical parameters such as temperature, salinity, density, dissolved oxygen, and apparent oxygen utilization is computed using the World Ocean Database (WOD18). The reliability of estimate is closely tied to the quality assurance of the in-situ observations and statistical interpolation schemes of the mapping. Therefore, in this context, WOD18 used for this study has gone through a non-linear quality control procedure developed by Shahzadi (2020) on a global domain. The mapping of resulting data is carried out using Data Interpolating Variational Analysis (DIVA). Sensitivity experiments are carried out to choose the key parameters of DIVA, namely the horizontal correlation lengths, and the Noise to Signal ratio (N/S). Furthermore, two new indices such as roughness index, and root mean square of residuals are designed to show the impact of the correlation length, and N/S ratio choices. For temperature and salinity, two different versions of the climatological estimates are produced: (i) a long-term (1900 to 2017) climatology using multiple platforms in-situ data, and (ii) a shorter time estimate (2003-2017) using data from ocean drifting platforms such as profiling floats. The two versions are intercompared and differences are evaluated. &amp;#160;Similar procedures are applied for global mapping of Density, Oxygen, and Apparent Oxygen utilization. The new climatological estimates are compared with previous estimates such as World Ocean Atlas and World Argo Global Hydrographic climatological estimates, and thereby the differences are analysed.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords:&lt;/strong&gt; WOD18, temperature, salinity, apparent oxygen, DIVA, climatology, non-linear quality control.&lt;/p&gt;&lt;p&gt;Shahzadi, K., (2020): &amp;#8220;A New Global Ocean Climatology&amp;#8221;, Ph.D. Thesis (under evaluation), University of Bologna, Italy, pp. (19-35. of pages)&lt;/p&gt;

OKSIGEN TERLARUT DAN APPARENT OXYGEN UTILIZATION DI PERAIRAN WAIGEO BARAT, RAJA AMPAT

Pengamatan kadar oksigen terlarut telah dilaksanakan di perairan Waigeo Barat, Raja Ampat, Papua Barat. Penelitian ini bertujuan untuk mengetahui kondisi oksigen terlarut dan Apparent Oxygen Utilization (AOU). Hasil analisa menunjukkan bahwa kadar oksigen terlarut di lapisan permukaan, 5 meter dan dekat dasar masing-masing berkisar antara 5.90-8.48 mg/l; 6.06-8.04 mg/l dan 6.12-7.98 mg/l. Berdasarkan nilai suhu dan salinitas yang diperoleh dari penelitian ini telah dihitung daya larut, derajat kejenuhan oksigen dan nilai AOU. Di lapisan permukaan nilai AOU berkisar antara (-0.01)-2.77 mg/l, di kedalaman 5 meter dan dekat dasar nilai AOU positif masing-masing berkisar antara 0.10-2.06 mg/l dan (0.16)-1.99 mg/l. Konsentrasi oksigen terlarut di perairan Waigeo Barat, Raja Ampat, belum menunjukkan dampak negatif terhadap lingkungan perairan dan masih sesuai dengan baku mutu air laut untuk biota laut. Kata kunci: Oksigen terlarut, AOU, Salinitas, Waigeo Barat, Raja Ampat

Dissolved Oxygen and Apparent Oxygen Utilization in Lembeh Strait Waters, North Sulawesi

The observation of dissolved oxygen level and Apparent Oxygen Utilization (AOU) in Lembeh Strait Waters was conducted in January, February, June and July 2016. The objective of this research is to know the condition of dissolved oxygen and Apparent Oxygen Utilization (AOU). The results of the analysis showed that dissolved oxygen levels in the surface layer and near the bottom ranged from 6.00-6.56 mg/l and 5.59-6.17 mg/l. Based on the values of temperature and salinity obtained from this study, solubility, oxygen saturation degree and AOU value at the surface layer were calculated. In the surface layer the AOU values are positive, ranging from 0.10-0.72 mg/l, while near the bottom, negative and positive AOU values were balanced, ranging from -0.23-0.42 mg/l. The concentration of dissolved oxygen in the Lembeh Strait waters has not shown negative impact on the aquatic environment and is still in accordance with sea water quality standards for marine biota.Keywords: Dissolved oxygen, apparent oxygen utilization (AOU), Lembeh Strait. ABSTRAK Pengamatan kadar oksigen terlarut dan Apparent Oxygen Utilization (AOU) di Perairan Selat Lembeh dilaksanakan pada bulan Januari, Februari, Juni dan Juli 2016. Penelitian ini bertujuan untuk mengetahui kondisi oksigen terlarut dan Apparent Oxygen Utilization (AOU). Hasil analisa menunjukkan bahwa kadar oksigen terlarut di lapisan permukaan dan dekat dasar berkisar antara 6,00-6,56 mg/l dan 5,59-6,17 mg/l. Berdasarkan nilai suhu dan salinitas yang diperoleh dari penelitian ini telah dihitung daya larut, derajat kejenuhan oksigen dan nilai AOU pada lapisan permukaan. Di lapisan permukaan nilai AOU semuanya positip berkisar antara 0,10-0,72 mg/l dan di dekat dasar nilai AOU negatip dan positip berimbang, berkisar antara -0,23-0,42 mg/l. Konsentrasi oksigen terlarut di perairan Selat Lembeh belum menunjukkan dampak negatip terhadap lingkungan perairan dan masih sesuai dengan baku mutu air laut untuk biota laut. Kata Kunci: Oksigen terlarut, apparent oxygen utilization (AOU), Selat Lembeh.

Spatial variability of nitrous oxide in the Minho and Lima estuaries (Portugal)

Nitrous oxide (N2O) is a potent long-lived greenhouse gas and estuaries represent potentially important sources of this biogas to the atmosphere. In this work, we analyse the first N2O data obtained in the Minho and Lima estuaries, and the processes and environmental factors that may regulate its production in these systems. In September 2006, N2O attained values of up to 20.0 nmol L–1 in the upper reaches of the Lima estuary and the river was, apparently, the main source of biogas to the system. In Minho N2O reached a maximum of 14.4 nmol L–1 and nitrification appeared to contribute to the enhancement of N2O. In the upper estuary, the relatively high concentrations of nitrification substrate NH4+, the positive correlations found between N2O level above atmospheric equilibrium (ΔN2O) and apparent oxygen utilization and NO2–, and the negative correlations between ΔN2O and NH4+ and pH can be interpreted as in situ N2O production through pelagic nitrification. Principal component analysis gave evidence of considerable differences between upper estuaries, particularly in terms of higher N2O in Lima and NH4+ in Minho. Surface waters of both estuaries were always N2O-supersaturated (101-227%) and estimated N2O emissions from Minho and Lima were 0.28 Mg N2O-N yr–1 and 0.96 Mg N2O-N yr–1, respectively, which represent a reduced fraction of N2O global emission from European estuaries.

Seasonal variation of CaCO₃ saturation state in bottom water of a biological hotspot in the Chukchi Sea, Arctic Ocean

Distribution of calcium carbonate saturation state (Ω) was observed in the Chukchi Sea in autumn 2012 and early summer 2013. Ω in bottom water ranged from 0.3 to 2.0 for aragonite and from 0.5 to 3.2 for calcite in 2012. In 2013, Ω in bottom water was 1.1–2.8 for aragonite and 1.7–4.4 for calcite. Aragonite and calcite undersaturation was found in high productivity regions in autumn 2012 but not in early summer 2013. Comparison with other parameters has indicated that biological processes – respiration and photosynthesis – are major factors controlling the regional and temporal variability of Ω. From these ship-based observations, we have obtained empirical equations to reconstruct Ω from temperature, salinity and apparent oxygen utilization. Using 2-year-round mooring data and these equations, we have reconstructed seasonal variation of Ω in bottom water in Hope Valley, a biological hotspot in the southern Chukchi Sea. Estimated Ω was high in spring and early summer, decreased in later summer, and remained relatively low in winter. Calculations indicated a possibility that bottom water could have been undersaturated for aragonite on an intermittent basis even in the pre-industrial period, and that anthropogenic CO2 has extended the period of aragonite undersaturation to more than 2-fold longer by now.

OKSIGEN TERLARUT DI SELAT LOMBOK

Oksigen merupakan gas penting dalam perairan laut dan berperan dalam proses biogeokimia laut. Sumber oksigen berasal dari difusi dari udara melalui proses turbelensi dan hasil fotosintesis. Penelitian ini bertujuan untuk mengkaji distribusi dan pengaruh Indonesian Throughflow (ITF) terhadap konsentrasi oksigen terlarut di Selat Lombok. Sebanyak 11 stasiun (3 di utara; 6 di tengah; 2 di selatan) dianalisis kandungan oksigen terlarutnya dengan menggunakan metode modifikasi winkler. Hasil analisis menunjukan bahwa kandungan oksigen di bagian utara berkisar 2,48-7,15 mg/l, tengah 2,32-6,58 mg/l dan selatan 2,35-6,71 mg/l. Berdasarkan nilai apparent oxygen utilization (-2,70–5,64 mg/l) dan normal atmospheric equilibrium concentration (3,84-7,96 mg/l), mencerminkan kandungan oksigen yang semakin berkurang pada lapisan permukaan. AOU dan NAEC secara implisit berubah terhadap kedalaman dimana konsentrasinya akan semakin tinggi dengan bertambahnya kedalaman. Hasil pengukuran suhu dan salinitas menunjukan bahwa Selat Lombok mempunyai suhu dan salinitas masing-masing berkisar antara 4,74-30,080C dan 33,48-34,78 psu. Analisis TS-diagram menunjukan terdapat dua massa air yang membawa kandungan oksigen di Selat Lombok yaitu Northern Subtropical Lower Water (NSLW) (salinitas=34,53-34,58 psu, suhu=13,57-15,06 0C; sigma-t (s t)=25,40-25,80)) dan Northern Pacific Intermediate Water (NPIW) (salinitas=34,48-34,54 psu; suhu=6,30-7,90 0C; sigma-t (s t)=26,70-27,20). NSLW ditemukan pada kedalaman 100-180 (utara), 100-550 m (tengah) dan 190-220 m (selatan), sedangkan NPIW tidak terlihat dengan menggunakan pendekatan oksigen terlarut dan hanya bisa dilihat dengan pendekatan suhu dan salinitas.