Fernando Siringan | University of the Philippines (original) (raw)

Papers by Fernando Siringan

Quaternary International, Aug 1, 2017

Microbial carbonates (microbialites) occurred in the Holocene coral reefs at Paraoir, the Philipp... more Microbial carbonates (microbialites) occurred in the Holocene coral reefs at Paraoir, the Philippines. These microbialites appeal grayish to buff in color with a stromatolitic to thrombolitic structures, and encrust on corals directly or on a thin layer of calcareous red algae or encrusting foraminifera that covered the corals first. The microbialites only occur in the lower (earlier) parts of the Holocene reef sequence where Heliopora coerulea dominated. No microbial carbonates were observed in the upper (younger) part of the Holocene reefs that is interpreted to grow in water depth shallower than 6 m on the basis of coral community. Samples of microbial carbonate and associated coral were dated by AMS 14 C. The results show that the microbialites formed about 10 to 7.5 kyr BP, nearly coeval to or a few hundred years younger than the corals on which the microbialites encrusted. AMS 14 C ages of samples recovered at reef margins are consistent to 230 Th ages of corals associated with the microbialites, but those recovered in the back reef are much older that the previously published 230 Th ages of corals and interpreted to be reworked into the backreef. It is proposed that the microbialites at Paraoir formed in early Holocene on reef slope when the deglacial sea level was rising rapidly. After 7.5 kyr BP when the sea-level rise slowed down and coral reefs caught up with sea level, the condition became favorable to corals prospered in shallow water, and no longer suitable for microbialite formation.

Palaeogeography, Palaeoclimatology, Palaeoecology, Nov 1, 2022

This dataset includes total organic carbon (TOC), total nitrogen (TN), stable carbon isotope (δ13... more This dataset includes total organic carbon (TOC), total nitrogen (TN), stable carbon isotope (δ13C) and radiocarbon activity (expressed as fraction modern - Fm) of TOC, as well as mineral surface area (SA) and grain size of 44 sediment samples from 28 rivers on Luzon of Philippines. The samples were collected during July 2007. TOC, TN, and stable δ13C of carbonate-free sediments were measured by an elemental analyzer interfaced with an isotope ratio mass spectrometer (EA-IRMS; Flash EA 1112 HT-Delta V Advantage). Duplicate analyses of three samples show the reproducibility of TOC, TN, and δ13C are ±0.02%, ±0.01% and ±0.02‰, respectively. Radiocarbon measurements of TOC were performed on an accelerator mass spectrometer (AMS) at the Laboratory of Ion Beam Physics, ETH Zürich. The results are reported as fraction modern (Fm). The absolute error of Fm values for all samples is better than ±0.01. SA of sediments were determined using 5-point Brunauer-Emmet-Teller (BET) N2 adsorption iso...

Frontiers in Earth Science, 2022

The 1994 Mw 7.1 Mindoro Earthquake and the 2017 Mw 5.9 Batangas Earthquake Sequence both occurred... more The 1994 Mw 7.1 Mindoro Earthquake and the 2017 Mw 5.9 Batangas Earthquake Sequence both occurred in offshore southern Batangas and devastated southern Luzon and Mindoro. These earthquakes exhibited NW-striking right-lateral slip in an area presumably defined by a WNW-striking left-lateral fault, therefore implying the existence of previously unmapped offshore faults. High resolution multibeam bathymetry grid and subbottom profiles revealed a conjugate strike-slip fault system under an approximately EW-directed extension. NW-striking right-lateral faults (F1 Faults: Central Mindoro Fault, Aglubang River Fault, and Batangas Bay Fault System) bound the western part of the study area. On the other hand, a series of almost parallel NE-trending left-lateral and normal faults (F2 Faults: Macolod Corridor, North Verde Fault System, Central Verde Fault System, South Verde Fault, and Northeast Mindoro Fault System) approach the F1 faults from the northeast. The distribution of the 1994 and 2...

&lt;p&gt;The northwestern coast of Luzon Island is located within the forearc reg... more &lt;p&gt;The northwestern coast of Luzon Island is located within the forearc region of the Manila Trench where emergent coral reef platforms have been reported; and an uplift rate of 0.5 m/kyr has been estimated for the past 7,000 years in San Fernando and Currimao. This study examined the present-day vertical land movement (VLM) in both sites using tide gauge records and retracked Jason satellite altimeter missions. Both the tide gauge and satellite data were corrected for tides using the T_Tide algorithm and the difference between the tide gauge sea level (TGSL) and sea surface heights (SSH) from the satellite were calculated. The influence of VLM was inferred from the differences between the TGSL and SSH, then validated using available GNSS data.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Hourly TGSL for San Fernando is available from 2002 to 2018 with a completeness index (CI) of 37%. The satellite products used were the 20 Hz MLE4 and 1Hz ALES retracked Jason satellite series downloaded from AVISO+ and OpenADB, respectively. The MLE4 product indicates subsidence with a rate of 0.43 &amp;#177; 0.10 mm/yr, while ALES indicates uplift at 1.93 &amp;#177; 0.42 mm/yr. GNSS observations at the San Fernando TG benchmark (TGBM) from 2017 to 2019 shows subsidence at 0.74 &amp;#177; 0.40 mm/yr, which agrees well with the VLM estimate from the difference between TGSL and MLE4 SSH.&amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Currimao TG station has a CI of 90% from 2008 to 2016. Satellite products used were the 20 Hz MLE4 and 20 Hz ALES retracked Jason-2 downloaded from AVISO+, and both indicate uplift with a rate of 7.30 &amp;#177; 0.17 and 6.24 &amp;#177; 0.25 mm/yr, respectively. The present-day uplift agrees with the geological records, however, there are no GNSS data at the TGBM to validate the present-day vertical motion.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The differences between the present-day vertical motion of San Fernando and Currimao may indicate the influence of other fault systems associated with the Philippine Fault or segmentation of the forearc. Subsidence in San Fernando could imply stress accumulation in the area and the observed uplift in the geological records are cumulative co-seismic vertical displacements.&amp;#160;&amp;#160;&lt;/p&gt;

Journal of Asian Earth Sciences, 2016

Abstract Shallow-water corals are crucial natural archives for reconstructing deglacial sea-level... more Abstract Shallow-water corals are crucial natural archives for reconstructing deglacial sea-level changes. However, significant discrepancies exist between sea-level records from different places. Here we present recently acquired 230 Th-dated coral ages between 10,256 ± 50 yr BP and 6654 ± 29 yr BP (before 1950 AD) from Paraoir, western Luzon, Philippines to document deglacial sea-level rise of the western Pacific. The results indicate that the Paraoir reef started growing 10.3 kyr BP from about 29 m below present sea level, and reached 8 m below the PSL at 7.2 kyr BP. The Paraoir sea-level records are consistent with those of northwestern Luzon and the western Australia coast; both of which are coral-based records in continental or island arc settings. But sea levels of Luzon are significantly higher than those of Tahiti, a basaltic island on oceanic crust. We propose that the differences in sea level between the Philippine and Tahiti result from spatial variations of glacial isostatic adjustment of the two sites.

Phycological Research, 2004

The lateral variation of sediment properties and associated cyst content of sediment in Manila Ba... more The lateral variation of sediment properties and associated cyst content of sediment in Manila Bay were determined and their possible role/s in the occurrences of Pyrodinium bahamense Plate var. compressum (Böhm) Steidinger, Tester et Taylor toxic blooms were assessed. Manila Bay's surface sediment was determined to be silt dominated. Clay generally increased towards the coast, probably as a result of flocculation and rapid deposition upon entry of sediments from the rivers. High sand content characterized the southeastern part of the bay attributed to the greater sand inputs and relatively strong currents in this area. Bulk densities were lower in the eastern side of the bay from dilution by high organic load from sewage and urban areas. Benthic flux calculations, particularly NH3, suggest more than 50% nutrient contribution comes from sediments. In general, dinoflagellate cyst density increased from the center of the bay towards the coast, except in Pampanga Bay where it decreased near the coasts. A maximum of 23 dinoflagellate species were identified: 5 were autotrophic (Lingulodinium polyedrum (Stein) Dodge , Gonyaulax spp., Pyrophacus steinii (Schiller) Wall et Dale , Protoceratium reticulatum (Claparéde et Lachmann) Bütschli , and Pyrodinium bahamense var. compressum), and the rest were predominantly composed of Protoperidinium spp. and Diplopsalis spp. Heterotrophs comprised about 70% of the total cyst counts. Pyrodinium counts increased towards the northwestern part of the bay where it was the dominant autotroph species. Negative correlations were observed for live Pyrodinium cyst density and N flux, P flux, ratio of N to P and total organic carbon (TOC) content. However, areas with high N:P ratio contain abundant Pyrodinium live cysts.

Harmful Algae, 2008

Temporal variation in the type and abundance of dinoflagellate cysts in Manila Bay, Philippines, ... more Temporal variation in the type and abundance of dinoflagellate cysts in Manila Bay, Philippines, is established using 210Pb-dated sediment cores. At least 17 dinoflagellate cyst species, including those of the toxic species, Pyrodinium bahamense var. compressum, were identified. P. bahamense may have been present in the area since at least the 1920s. Total cyst density has increased beginning about 1988

Environmental Pollution, 2011

Organophosphorus compounds (OPCs) and stable isotope ratios (d 13 C and d 15 N) were determined i... more Organophosphorus compounds (OPCs) and stable isotope ratios (d 13 C and d 15 N) were determined in 58 fishes belonging to 20 species collected from Manila Bay, the Philippines. OPCs were detected in most of the samples and found up to mg/g lw (lipid weight) level, suggesting their ubiquitous presence in the coastal marine environment of the Philippines. Higher levels (>1000 ng/g lw) of total OPCs were determined in yellowstriped goatfish, silver sillago, tripletail wrasse and bumpnose trevally indicates either their active uptake from ambient water or lower metabolic capacity of these species. Levels of triphenyl phosphate (TPhP) in demersal species showed a positive correlation with d 15 N, indicating that TPhP was adsorbed onto the particle, settled down to the bottom sediment and accumulated through the benthic food web rather than the pelagic. Estimated dietary intake of OPCs in Manila Bay fishes were four to five orders of magnitude lower than the proposed reference dose (RfD).

Climatic Change, 2012

Abstract Coral reefs and other coastal ecosystems such as seagrasses and mangroves are widely rec... more Abstract Coral reefs and other coastal ecosystems such as seagrasses and mangroves are widely recognized to provide protection against the devastating effects of strong waves associated with tsunamis and storms. The predicted warming climate brings to fore the ...

Bulletin of Volcanology, 2007

... C. Remotigue .P. Zamora .R. Rodolfo National Institute of Geological Sciences, College of Sci... more ... C. Remotigue .P. Zamora .R. Rodolfo National Institute of Geological Sciences, College of Science, University of the Philippines Diliman, Quezon City 1101, Philippines e-mail ... So also are flash floods suddenly released from lakes in volcano craters and calderas (Bernard 1994). ...

Quaternary International, 2014

In recent decades, eutrophication has been identified as a major problem in coastal and estuarine... more In recent decades, eutrophication has been identified as a major problem in coastal and estuarine systems. Eutrophication can be due to cultural activities but can also be due to natural factors. This study explores the possible role of geomorphic change in the eutrophication history of Juag Lagoon, which is one of the sites with harmful algal blooms in the Philippines. Surface and sediment cores were acquired for this study to trace the paleoenvironmental changes that brought about the present day lagoon. Radiocarbon dates and 210 Pb-based estimates of sedimentation rates provided age control. Sedimentological indicators and stable isotope signatures of organic matter were utilized to assess changes in the source of organic matter deposited in the lagoon whereas XRF-derived bulk sediment geochemistry was used as proxy for sediment input. Three phases of geomorphic state were identified over the lagoon history. Prior to 700 A.D., bulk geochemistry and isotopic measurements indicate a prelagoon environment. Subsequent drop in sea level led to the development of the lagoon, which persisted until 1100 A.D. The lagoonal condition transitioned to increased marine influence towards 1200 A.D., through several sandbar-breaching events that may have persisted in recent years. The present day lagoon maintains a continuous water exchange through a small tidal channel. The closing of the lagoon and the limited flushing of lagoon waters could have led to the nutrification of the lagoon. Moreover, anthropogenic impact through forest denudation, mariculture and fertilizer use in the neighboring islands is reflected, which could have also affected the nutrification of the lagoon in the last 100 years.

Although a major potential contributor to water and nutrient budgets, lacustrine groundwater disc... more Although a major potential contributor to water and nutrient budgets, lacustrine groundwater discharge (LGD) is often neglected in most lake studies. Through electrical resistivity profiling surveys, the authors examined the possible occurrence of LGD in southern Laguna de Bay, the largest freshwater lake in the Philippines. Discrete and dispersed LGDs were identified. Discrete LGDs were inferred from narrow highly resistive zones that cut vertically across the lake floor. These discrete LGDs line-up with projections of lineaments on land and are thus deemed to be fault-controlled. Dispersed LGDs, interpreted from wide swaths of resistivity signals cutting across the lake floor, were found to occur more commonly in shallower areas. Findings from radon concentrations, nutrient concentrations, and chlorophyll a analyses support the perceived patterns of LGD occurrences. Nutrient input through LGD is probably contributing to the lake’s current eutrophic condition however where discrete...

Manila Bay has a wide range of environmental problems that need to be addressed — from land-based... more Manila Bay has a wide range of environmental problems that need to be addressed — from land-based and sea-based sources of pollution to harmful algal blooms, subsidence and groundwater extraction, overexploitation of fishery resources, and habitat conversion and degradation. However, there are reasons to be optimistic. There is greater accountability expected of public officials vis-a-vis environmental laws, significant and increasing

… climate change and …, 2006

Science Diliman, 2007

Uncontrolled groundwater extraction has been proposed as the main cause of accelerated subsidence... more Uncontrolled groundwater extraction has been proposed as the main cause of accelerated subsidence in the delta region north of Manila Bay. However, natural autocompaction of deltaic sediment and other anthropogenic factors also enhance subsidence, amplifying global sea-level rise and aggravating land loss, flooding, and tidal inundation. Here, we report how we determine the longer-term subsidence rates and paleo-sealevel history of the delta plain using sediment cores. Four sediment cores 3 to 10.7 m long taken in Bocaue and Malolos, Bulacan and Lubao, Pampanga all display shoaling-upward sequences that consist of, from bottom to top: basal shallow-marine clays comprising nearly half of each core; mangrove peat; beach sand; fluvial sand and mud; and uppermost floodplain clays. Porosities of the deltaic sediments range from 0.3 to 0.8. Peat has the highest porosities, from 0.7 to 0.8. Calculations indicate about 2 to 6 m of compaction for the whole sediment sequence. Wood fragments at 7 m and 8.4 m depths in the shallow-marine section of the Pampanga core respectively yielded radiocarbon ages of 1800 ± 40 and 1730 ± 40 years. If around 1,000 years ago is when the surface 10 m of sediments started compacting, they would have done so at rates of 0.2 to 0.6 cm/y. Natural compaction in similar environments such as in Po Delta, Italy and Mississippi Delta are comparable, ranging from 0.09 to 0.37 cm/y. The small values acquired in this study imply that large human-induced components may account for as much as 97 percent of the subsidence in Pampanga.

Journal of Sedimentary Research, 2004

The low gradient east Texas coast and inner-continental shelf, from Sabine Lake at the Texas-Loui... more The low gradient east Texas coast and inner-continental shelf, from Sabine Lake at the Texas-Louisiana border to the western end of Galveston Island, experienced extreme along-strike variations in rates of Holocene coastal retreat. Around 7.7 ka a barrier shoreline was located approximately 55 km offshore. Toward the western end of Galveston Island, the shoreline retreated 55 km, occupying a position on the lagoon side of the Island by about 5.3 ka. Toward the Texas-Louisiana border, the shoreline retreated more gradually, ...

&amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;gt;Submarin... more &amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;gt;Submarine groundwater discharge (SGD) is any direct flow of fluid across the seafloor, which forms bubbly or leaky springs and seeps from the intertidal zone to the deep sea. SGDs can significantly alter physico-chemical conditions of seepage zones. Identifying and mapping SGD is crucial to further recognize its influence in both marine and terrestrial ecosystems. However, mapping this phenomenon has been a continuing challenge, mainly due to the difficulty in its detection and quantification. This study explores the capability and applicability of an inexpensive, commercially available, recreational-grade combination of depth meter and side scan sonar system to image different types and identify point sources of coastal SGDs. Standard and systematic methodologies for efficient imaging and processing were established. The utility of the recreational-grade system was assessed and validated using a research-grade side scan sonar. SCUBA diving and CTD casting were conducted for ground-truthing and further characterization. Lower frequency sonars (83/200 kHz) showed more distinct acoustic signatures of discrete and dispersed bubbly SGDs, than the higher frequency system (455 kHz and 780 kHz research-grade unit). Sonar images showed that SGD plumes can be indicated by near seafloor to midwater cloud-like features. Spring-type SGDs tend to form cloud features with a funnel-shaped morphology. In sites where SGDs are dispersed, the acoustic signature is a curtain-like cloud, with higher bubble density in the upper water column. This is consistent with diver-based observation of increasing bubble sizes (&amp;amp;amp;amp;amp;amp;amp;amp;lt;1 mm to ~30 mm) from point source to water surface. CTD casts indicate that the SGDs have recirculated seawater, with increasing temperature and salinity with depth. In the assessment of system and data processing requirements, and costing, a recreational-grade unit provides a good alternative for coastal SGD works.&amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;gt;