Volume Two May 2014 Appendix 12 Natural Sedimentation on the Chatham Rise (Nodder 2013) Natural Sedimentation on the Chatham Rise Prepared for Chatham Rock Phosphate LLtd August 2012 (Updated April 2013) Authors/Contributors: Scott D. Nodder For any information regarding this report please contact: Scott Nodder Group Manager/Marine Geologist Ocean Geology +64-4-386 0357 [email protected] National Institute of Water & Atmospheric Research Ltd 301 Evans Bay Parade, Greta Point Wellington 6021 Private Bag 14901, Kilbirnie Wellington 6241 New Zealand Phone +64-4-386 0300 Fax +64-4-386 0574 NIWA Client Report No: WLG2012-42 Report date: August 2012 (Updated April 2013) NIWA Project: CRP12302/6 Remote sensing image of spring chlorophyll a concentrations in the New Zealand region [NASA/Orbimage/NIWA] (left) and sediment trap used for measuring sinking particle fluxes. [Scott Nodder, NIWA]. © All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). Such permission is only to be given in accordance with the terms of the client’s contract with NIWA. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system. Whilst NIWA has used all reasonable endeavours to ensure that the information contained in this document is accurate, NIWA does not give any express or implied warranty as to the completeness of the information contained herein, or that it will be suitable for any purpose(s) other than those specifically contemplated during the Project or agreed by NIWA and the Client. 26 April 2013 8.06 p.m. Contents Executive summary ................................................................................................................ 5 1 Objectives ...................................................................................................................... 7 2 Surficial sediments of the Chatham Rise: general characteristics .......................... 7 2.1 Grain-size distribution ............................................................................................ 7 2.2 Sediment composition ........................................................................................... 7 2.3 Sediment composition ........................................................................................... 8 2.4 Carbonate content ................................................................................................. 9 2.5 Organic content ..................................................................................................... 9 2.6 Sedimentation rates ............................................................................................... 9 2.7 Near-surface geological formations and authigenesis ......................................... 10 3 Natural sedimentation: origins and processes ........................................................ 10 3.1 Vertical fluxes ...................................................................................................... 11 3.2 Horizontal fluxes .................................................................................................. 16 3.3 Authigenesis ........................................................................................................ 17 4 Water column suspended particles and turbidity .................................................... 18 5 Comparison to other “deep-sea” studies ................................................................. 23 6 Conclusions ................................................................................................................ 24 7 Acknowledgements .................................................................................................... 25 8 References ................................................................................................................... 25 Figures Figure 2-1: NIWA 1:1 million scale Sediment chart, highlighting surficial sediment distributions on the Chatham Rise and in the Bounty Trough (McDougall, 1982). 8 Figure 3-1: Particulate fluxes in subtropical waters, just to the north of the Chatham Rise, east of New Zealand (station U940), in austral autumn, 1992 (reproduced from Figure 4, Nodder, 1997). 12 Figure 3-2: Average total mass (left) and particulate phosphorus (right) fluxes in different water types across Chatham Rise in winter (A) and spring (B). 13 Figure 3-3: Re-plotted data from Zhou et al. (2012) showing the spatial distribution of 234Th and POC fluxes on Chatham Rise. 15 Figure 4-1: Full water column nephelometer profiles on the crest (U941, left) and northern flank of the Chatham Rise (U943, U944 and U949). 19 Natural Sedimentation on the Chatham Rise Figure 4-2: Water column profiles of suspended particulate matter concenttrations on the northern flank of the Chatham Rise. 20 Figure 4-3: Fluorescence (top left panel) and beam transmission (right) profiles from CTD data collected on the crest of the Chatham Rise. 22 Reviewed by Approved for release by Helen Neil Julie Hall Natural Sedimentation on the Chatham Rise Executive summary The report summarises the natural sedimentation processes on the Chatham Rise in order to provide background information to the proposed phosphorite sea-bed mining operations of Chatham Rock Phosphate (CRP) Ltd. The sediments on the crest of the Chatham Rise are predominantly phosphorite-bearing, glauconitic, fine- to medium-grained, foraminiferal sandy muds or muddy sands, with subsidiary phosphorite nodules (typically part of the >5% gravel component), rock fragments, volcanic ash, clay minerals and biogenic material. Calcium carbonate percentages of these surficial sediments are typically 30-40% with organic carbon levels of 0.5-1%. These surface sediments are considered to represent a condensed sequence, representing a long period of time preserved in a relatively thin layer of material (typically <10 m thick). Downward vertical fluxes of material on the crest of the Chatham Rise within the Subtropical Front are generally elevated compared to the water masses on either side of the rise, reflecting the highly productive nature of the frontal zone. Vertical fluxes on the rise are in the order of 180-500 mg/m2/d, but have been measured as high as 1800 mg/m2/d close to the sea-floor. These vertical flux values indicate that the Chatham Rise has fluxes that are similar in magnitude to other temperate, continental margin and open ocean environments. Sinking particles are affected by currents that can move them horizontally away from their point of origin, and such near-bed currents can also be sufficient to resuspend and transport bottom sediments. Measurements of water column turbidity, including recent mooring data collected by IX Survey for CRP Ltd, show that increases in turbidity are a prominent feature close to the Chatham Rise sea-floor, with values as high as 0.55 mg/l on the crest of the rise. While the report summarises the information available on natural sedimentation on the Chatham Rise crest, there is actually very limited temporal and spatial information on the magnitude and timing of episodic flux events in this region. In particular, information is lacking on how water column particulate populations and sea-floor sediments on the crest interact with the dynamic physical environment within the Subtropical Front over a variety of temporal (days to years) and spatial (1 to 100’s of km) scales. Natural Sedimentation on the Chatham Rise 5 1 Objectives In July 2012, the National Institute of Water and Atmospheric Research (NIWA) Ltd was contracted by Chatham Rock Phosphate (CRP) Ltd to undertake a review of natural sedimentation on the Chatham Rise. The review is designed to provide background information on the present-day sedimentary system on the rise in the context of CRP’s proposed sea-bed mining operations for phosphorite nodules. The objectives of this report are to: . Describe natural sedimentation of particulate matter on the Chatham Rise; . Overview natural sediment producing processes and nature of particulates; . Overview studies/identify locations where turbidity/TSS etc. data from on the Chatham Rise and nearby; . Overview water column particulate data/turbidity from the various data sources above, including IX data; . Overview sedimentation studies and the data available from those studies; and . Comment on ‘deep sea’ data (similar depths) where data might provide useful comparative data. 2 Surficial sediments of the Chatham Rise: general characteristics 2.1 Grain-size distribution The surface sediments on the Chatham Rise crest are predominantly sandy muds or muddy sands (~55-60% >63 µm), typically comprising 25-30% silt (63-4 µm, %mud = %silt + %clay) and ~5-10% clay (<4 µm) in the mud fraction (<63 µm) (e.g., Table 1 in Grove et al., 2006; also Appendix in Nodder et al., 2011) (also see comparable data in McDougall (1982) and von Rad and Rösch (1984)) (Figure 2-1). Detailed mapping by Lawless (2012) showed that, based on Folk’s (1968) classification, on the rise crest between 177°E and 180° the surficial sediments are predominantly sands on shallow highs (<250 m water depth), such as Reserve Bank, grading to silty sands and sandy silts at deeper sites (>250 m), with >5% gravel (mainly phosphorite nodules) east of 179°E. From previous studies, phosphorite nodules are typically in the 0.5->1 mm size-fraction, up to maximum nodule diameters of 50- 200 mm, increasing in size down-core towards the underlying Oligocene chalks (see