Comments to Angulo et al . 2016 on “ Sea-level fluctuations and coastal evolution in the state of Rio de Janeiro , southeastern-Brazil ” by Castro et al . 2014

Interpretation of sea-level indicators is essential when studying paleo sea-level fluctuations during the Holocene. Sea-level indicators may have different origins, such as geological (beachrocks) and biological (vermetids and barnacles). In order to reconstruct paleo sea-level, it is necessary to attribute an indicative meaning to each sea-level indicator. This paper aims to discuss issues raised by Angulo et al. (2016) regarding to the sea-level fluctuations curve proposed by Castro et al. (2014) to the Rio de Janeiro State coast, Brazilian southeast. The key issue that deserves posing is that local or regional curves cannot be built based on large scale (global) RSL geophysical models even in places of steady crust like Brazil. Here, we put into question the relative sea-level fluctuation curve model proposed by Angulo et al. (2006, 2016) to the coast of Rio de Janeiro State and Pernambuco State. It is strengthened the proposal of using different origins indicators on RSL vertical variation, georeferenced by high precision altitude GPS, adjusted by Brazilian Geodetic System benchmarks, maintained by the Brazilian Institute of Geography and Statistics IBGE. All issues regarding the curve drawn by Castro et al. (2014) are answered based on field data, laboratory analytical techniques, radiocarbon dating as well as relevant literature.


INTRODUCTION
We appreciate Angulo et al. (2016) comments and the opportunity to discuss some important aspects related to sea-level fluctuation and coastal evolution in southeastern Brazil.Data confrontation and controversy involving interpretation related to sea-level changes at the Brazilian coast during the Holocene are a challenge for the advancement of scientific knowledge about the subject.In the 1980s curves of relative sea-level changes worldwide during Holocene have revealed great surprises and brought up unconceivable discussions before that JOÃO WAGNER A. CASTRO et al. time.Among them the fact that there is no single curve of global variation even in regions of stable crust like Brazil (Martin et al. 1998).This finding has pushed for new researches aiming RSL curves all around the world.Suguio et al. (1985) have proposed that paleo sea-level have dropped from 4,0 m to 5,0 m in the last 5.500 years in the Brazilian east coast.The idea of paleo sea-level higher than the current during Holocene was accepted with a degree of reluctance since it was contrary to the United States east coast curve, which shows an ongoing ascension at the same time interval.
From the end of last century till nowadays divergences have arisen regarding data interpretation about relative sea-level curves at the Brazilian coast.Tomazelli et al. (1998) has sketched out a curve to Rio Grande do Sul State coast that diverges in some aspects from curves proposed by Suguio et al. (1985) for other regions along the Brazilian coast.The Rio Grande do Sul State curve shows that the sea would have risen in the last 2.000 yrs.According to curves of Salvador (Bahia State), Santos (São Paulo State) and Itajaí (Santa Catarina State) the sea-level would have dropped in the same time interval.Angulo et al. (2006) expressed doubts on the high frequency oscillations of 200 to 300 years proposed in those curves.Martin et al. (1998) have questioned the application of a single indicator for paleo sea-level reconstruction presenting a number of counterpoints and inconsistencies.Bezerra et al. (2003) developed an envelope curve of relative sea-level fluctuation in the coast of Rio Grande do Norte State, meso tide dominated, showing oscillations after maximum Holocene high stand, which occurred at ∼5000 cal yrs BP.This curve shows remarkable deviations compared with average curve to the central-south Brazilian coast.Castro et al. (2014) have proposed a RSL curve to Rio de Janeiro coast, involving the Holocene.From the very first time in the Brazilian coast it was identified a negative record of RSL in the late Pleistocene and early Holocene.As indicator it was used alignment of paleo beaches composed of submerged beachrocks.After that transition, a process of relatively fast sea-level rise started, like in other curves proposed to the Brazilian east coast.All indicators of RSL vertical variation identified, among them beachrocks, vermetids and barnacles, were georeferenced by high precision altitude GPS, adjusted by Brazilian Geodetic System benchmarks (RRNN), maintained by the Brazilian Institute of Geography and Statistics (IBGE).In order to mitigate the influence of possible sedimentological factors and regional tide gauge, the proposed curve was built on a restricted segment of the coast with relatively homogeneous oceanographical, geological and geomorphological characteristics.
One fact that stands out in Angulo et al. (2006Angulo et al. ( , 2016) ) is the altimetric data from ancient positions of relative sea-level were plotted based on a global model of curves made by geophysical simulations proposed by Milne et al. (2005) at the Caribbean and South America.Such model covers a wide geographical extension between Jamaica (Caribbean) and Beagle Channel (Argentina).In this model the spatial variation is dominated by the influence of ice and ocean mass redistribution on sea-level change with the ice-induced effect dominating the observed north -south trend (Milne et al. 2005) (Suguio et al. 1985, Martin et al. 1998, Bezerra et al. 2003, Castro et al. 2014, Cunha 2016).The Rio de Janeiro coastline is dominated by micro tide system with average spring tide of 0.90 m and neap tide between 0.06 and 0.025 m (Castro et al. 2014).The Pernambuco coastline is characterized by meso tide system with average spring tide of 2.0 m and neap tide of 0.7 m.Levels of reduced tide gauge in both places are different.Oceanographical, geological and geomorphological characteristics of both states are also completely different.Therefore, curves of such distinct coastline segments cannot be the same.The manuscript by Angulo et al. (2006) Peltier (1988) andthen Milne et al. (2005) which was applied in many places around the world including Rio de Janeiro and Pernambuco's coastline.Tide gauge levels in both coastal segments are distinct.Geological and oceanographical characteristics are also distinct, therefore the curve could not be the same for both sites.
We support the suggestion of using indicators from different origins when studying RSL vertical variation, especially beachrocks of the three inorganic categories above identified as well as vermetids of Dendropoma irregular and Petaloconchus varians species.Although Anomalocardia brasiliana mollusk shell does not provide accurate information about paleo sealevel vertical position, it could be useful to define upper limit (horizontal position) of ancient sealevel.The great sea flood caused by the maximum Holocene transgression in the Rio de Janeiro coastline is identified by the presence of mollusk shell deposited on the edge of ancient lagoon and bay systems.Every RSL indicators must be georeferenced by high precision altitude GPS and adjusted by Brazilian geodetic system benchmarks or other system with similar properties in other parts of the world.Therefore, RSL studies would be also useful when predicting future sea-level for coastal management programs.
Angulo et al. (2016)production of the geophysical simulation model initially proposed byPeltier (1988)and then byMilne et al. (2005).Factors such as fluvial sediment input in the inner continental shelf as well as tide gauge variations locally affect sea-level behavior.areforcedtostronglydisagreewithAngulo et al. (2016).We believe the data shown in our work were misinterpreted.Such criticism does not contribute for the scientific knowledge progress around the topic discussed.We must highlight the criticism made is not supported by field work in the Rio de Janeiro State coastline.We also believe that our results are convincing and have been used to support many doctoral and master theses.In this way, it contributes to better understanding of the relative sea-level fluctuations in the Rio de Janeiro coastline.Moreover, such research includes high precision altimetric data collection, scuba diving, laboratory analytical techniques and geochronological information complemented by clear and objective methodological procedures.The curve proposed by Angulo et al. (2006) to the Rio de Janeiro coastline reproduces the geophysical simulation model initially proposed by CONCLUSIONSUnfortunately, we