Unique Habitat for Benthic Foraminifera in Subtidal Blue Holes on Carbonate Platforms

Dissolution of carbonate platforms, like The Bahamas, throughout Quaternary sea-level oscillations have created mature karst landscapes that can include sinkholes and off-shore blue holes. These karst features are flooded by saline oceanic waters and meteoric-influenced groundwaters, which creates unique groundwater environments and ecosystems. Little is known about the modern benthic meiofauna, like foraminifera, in these environments or how internal hydrographic characteristics of salinity, dissolved oxygen, or pH may influence benthic habitat viability. Here we compare the total benthic foraminiferal distributions in sediment-water interface samples collected from <2 m water depth on the carbonate tidal flats, and the two subtidal blue holes Freshwater River Blue Hole and Meredith’s Blue Hole, on the leeward margin of Great Abaco Island, The Bahamas. All samples are dominated by miliolid foraminifera (i.e., Quinqueloculina and Triloculina), yet notable differences emerge in the secondary taxa between these two environments that allows identification of two assemblages: a Carbonate Tidal Flats Assemblage (CTFA) vs. a Blue Hole Assemblage (BHA). The CTFA includes abundant common shallow-water lagoon foraminifera (e.g., Peneroplis, Rosalina, Rotorbis), while the BHA has higher proportions of foraminifera that are known to tolerate stressful environmental conditions of brackish and dysoxic waters elsewhere (e.g., Pseudoeponides, Cribroelphidium, Ammonia). We also observe how the hydrographic differences between subtidal blue holes can promote different benthic habitats for foraminifera, and this is observed through differences in both agglutinated and hyaline fauna. The unique hydrographic conditions in subtidal blue holes make them great laboratories for assessing the response of benthic foraminiferal communities to extreme environmental conditions (e.g., low pH, dysoxia).

Features of Seasonal Sea Level Oscillations in the Russian Arctic Seas

Based on the analysis of long series of monthly mean sea level values from the database of the PSMSL and ESIMO portals, we obtained estimates of the mean and extreme amplitudes of seasonal oscillations. The mean amplitude of annual sea level oscillations in the White Sea is 7 cm, in the Barents Sea is 9–10 cm, in the Kara Sea, is 8–9 cm, in the Laptev Sea, is 10–11 cm, in the East Siberian and Chukchi seas is 13–14 cm. In the estuarine areas of seas, the amplitude of annual oscillations increases, and the semiannual, third-annual, and quarter-annual components appear in the sea level spectra. They are formed due to the asymmetry of the seasonal sea level variation with a sharp maximum during the flood period in June. Interannual changes in the amplitude of seasonal oscillations were identified and estimates of their extreme values were obtained. In some years, the amplitude of seasonal oscillations reaches 50 cm in the Yenisei Gulf and Gulf of Ob, 60 cm near the mouth of the Lena River, and 75 cm at the mouth of the Olenek River.

Minute Sea-Level Analysis (MISELA): a high-frequency sea-level analysis global dataset

Sea-level observations provide information on a variety of processes occurring over different temporal and spatial scales that may contribute to coastal flooding and hazards. However, global research on sea-level extremes is restricted to hourly datasets, which prevent the quantification and analyses of processes occurring at timescales between a few minutes and a few hours. These shorter-period processes, like seiches, meteotsunamis, infragravity and coastal waves, may even dominate in low tidal basins. Therefore, a new global 1 min sea-level dataset – MISELA (Minute Sea-Level Analysis) – has been developed, encompassing quality-checked records of nonseismic sea-level oscillations at tsunami timescales (T<2 h) obtained from 331 tide-gauge sites (https://doi.org/10.14284/456, Zemunik et al., 2021b). This paper describes data quality control procedures applied to the MISELA dataset, world and regional coverage of tide-gauge sites, and lengths of time series. The dataset is appropriate for global, regional or local research of atmospherically induced high-frequency sea-level oscillations, which should be included in the overall sea-level extremes assessments.

A first approach of the hydrological factors’ influence on the maritime navigation in the Black Sea

Efficient modern navigation is determined, among the other things, by the knowledge of the influence of the main hydrological factors on the movement of the ship, in different sea states. This paper aims to be a first approach on the influence of important hydrological factors such as waves, sea currents, sea level oscillations on navigation in an enclosed sea basin - the Black Sea, with specific physical geographical and hydrographic characteristics.

Seasonal and Decadal Variations of the Variance of the Synoptic and Mesoscale Sea Level Variability in the Baltic Sea

The present study examines the seasonal and decadal changes of the variance of the synoptic (periods from 2 days to 30 days) and mesoscale (periods from 2 h to 2 days) sea level oscillations in the Baltic Sea. Long-term hourly sea level records were used at 12 tide gauges located in different parts of the sea. We used spectral analysis to estimate the variance for different time scales. The spectral density of sea level oscillations in the Baltic Sea has maximum values in winter when the cyclonic activity in the atmosphere is more intensive. The maximum variances of synoptic σsyn2 and mesoscale σmes2 sea level oscillations are observed in winter, except for the heads of the Gulf of Finland (Gorny Institute) and Gulf of Riga (Pärnu), where the absolute maximum of σsyn2 is reached in November. The variances σsyn2 and σmes2 from November to February are 2–3 and 5 times higher than in the summer. The values of σsyn2 and σmes2 are characterized by high correlation up to 0.7–0.75 with wind variations and atmospheric indices (NAO, AO, and SCAND) in winter and low correlation in summer. The zonal wind and σmes2 in Gorny Institute are characterized by wide areas of high coherence at periods of 0.7–4 years. At Gedser, σsyn2 decreased by 19%, and at Ratan it increased by 17% over 90 years. The values of σmes2 over 90 years increased by 32% at Klagshamn, 36% at Ratan, and up to 60% at Kungsholmsfort.

MISELA: 1-minute sea-level analysis global dataset

Sea-level observations provide information on a variety of processes occurring over different temporal and spatial scales that may contribute to coastal flooding and hazards. However, global research of sea-level extremes is restricted to hourly datasets, which prevent quantification and analyses of processes occurring at timescales between a few minutes and a few hours. These shorter period processes, like seiches, meteotsunamis, infragravity and coastal waves, may even dominate in low-tidal basins. Therefore, a new global 1-minute sea-level dataset – MISELA (Minute Sea-Level Analysis) – has been developed, encompassing quality-checked records of nonseismic sea-level oscillations at tsunami timescales (T < 2 h) obtained from 331 tide-gauge sites (https://doi.org/10.14284/456, Zemunik et al., 2021b). This paper describes data quality-control procedures applied to the MISELA dataset, world and regional coverage of tide-gauge sites and lengths of time-series. The dataset is appropriate for global, regional or local research of atmospherically-induced high-frequency sea-level oscillations, which should be included in the overall sea-level extremes assessments.

Spatiotemporal structure of Baltic free sea level oscillations in barotropic and baroclinic conditions from hydrodynamic modelling

Free sea level oscillations in barotropic and baroclinic conditions were examined using numerical experiments based on a 3-D hydrodynamic model of the Baltic Sea. In a barotropic environment, the highest amplitudes of free sea level oscillations are observed in the northern Gulf of Bothnia, eastern Gulf of Finland, and south-western Baltic Sea. In these areas, the maximum variance appears within the frequency range corresponding to periods of 13–44 h. In a stratified environment, after the cessation of meteorological forcing, water masses relax to the equilibrium state in the form of mesoscale oscillations at the same frequencies as well as in the form of rapidly decaying low-frequency (seasonal) oscillations. The total amplitudes of free baroclinic perturbations are significantly larger than those of barotropic perturbations, reaching 15–17 cm. Contrary to barotropic, oscillations in baroclinic conditions are strongly pronounced in the deep-water areas of the Baltic Sea proper. Specific spatial patterns of amplitudes and phases of free barotropic and baroclinic sea level oscillations identified them as progressive–standing waves representing barotropic or baroclinic modes of gravity waves and topographic Rossby waves.

Analysis of the eastern Adriatic sea-level extremes

&lt;p&gt;The Adriatic Sea is known to be under a high flooding risk due to both storm surges and meteorological tsunamis, with the latter defined as short-period sea-level oscillations alike to tsunamis but generated by atmospheric processes. In June 2017, a tide-gauge station with a 1-min sampling resolution has been installed at Stari Grad (middle Adriatic Sea), the well-known meteotsunami hot-spot, which is, also, often hit by storm surges.&amp;#160;&lt;/p&gt;&lt;p&gt;Three years of corresponding sea-level measurements were analyzed, and 10 strongest episodes of each of the following extreme types were extracted from the residual series: (1) positive long-period (T &gt; 210 min) extremes; (2) negative long-period (T &gt; 210 min) extremes; (3) short-period (T &lt; 210) extremes. Long-period extremes were defined as situations during which sea level surpasses (is lower than) 99.7 (i.e. 2) percentile of sea level height, and short-period extremes as situations during which variance of short-period sea-level oscillations is higher than 99.4 percentile of total variance[J1]&amp;#160; of short-period series. A strong seasonal signal was detected for all extremes, with most of the positive long-period extremes appearing during November to February, and most of the negative long-period extremes during January to February. As for the short-period extremes, these appear evenly throughout the year, but strongest events seem to appear during May to July.&lt;/p&gt;&lt;p&gt;All events were associated to characteristic atmospheric situations, using both local measurements of the atmospheric variables, and ERA5 Reanalysis dataset. It was shown that positive low-pass extremes commonly appear during presence of low pressure over the Adriatic associated with strong SE winds (&amp;#8220;sirocco&amp;#8221;), and negative low-pass extremes are associated to the high atmospheric pressure over the area associated with either strong NE winds (&amp;#8220;bora&amp;#8221;), or no winds at all. On the other hand, high-pass sea level extremes are noticed during two distinct types of atmospheric situations corresponding to both &amp;#8220;bad&amp;#8221; (low pressure, strong SE wind) and &amp;#8220;nice&amp;#8221; (high pressure, no wind) weather.&lt;/p&gt;&lt;p&gt;It is particularly interesting that short-period extremes, of which strongest are meteotsunamis, are occasionally coincident with positive long-period extremes contributing with up to 50 percent to total sea level height &amp;#8211; thus implying existence of a double danger phenomena (meteotsunami + storm surge).&amp;#160;&lt;/p&gt;