AT Atlantic Power Corporation

The following constitutes Amendment No. 8 to the Schedule 13D filed by the undersigned (“Amendment No. 8”). This Amendment No. 8 amends the Schedule 13D as specifically set forth herein.

Item 2 is hereby amended and restated to read as follows:

(a)       This statement is filed by:

Each of the foregoing is referred to as a “Reporting Person” and, collectively, as the “Reporting Persons.” Each Reporting Person is a party to that certain Joint Filing Agreement, as further described in Item 6. Accordingly, the Reporting Persons are hereby filing a joint Schedule 13D.

Set forth on Schedule A annexed hereto (“ Schedule A ”) is the name and present principal business, occupation or employment and the name, principal business and address of any corporation or other organization in which such employment is conducted of the directors of Mangrove Master Fund, Mangrove Fund Cayman, Mangrove Capital and Mangrove Capital II. Mr. August is the sole director of Mangrove Partners. To the best of the Reporting Persons’ knowledge, except as otherwise set forth herein, none of the persons listed on Schedule A beneficially owns any securities of the Issuer or is a party to any contract, agreement or understanding required to be disclosed herein.

(b)       The address of the principal office of each of Mangrove Fund, Mangrove Partners, Mangrove Capital, Mangrove Capital II and Mr. August is 645 Madison Avenue, 14th Floor, New York, New York 10022. The address of the principal office of each of Mangrove Master Fund, Mangrove Fund Cayman, Mangrove Fund Cayman Drawdown and Mangrove Fund Cayman Partnership is c/o Maples Corporate Services, Ltd., P.O. Box 309, Ugland House, South Church Street, George Town, Grand Cayman, Cayman Islands KY1-1104.

(c)       The principal business of Mangrove Master Fund is acquiring, holding and disposing of investment securities. The principal business of Mangrove Fund is investing in Mangrove Master Fund. The principal business of Mangrove Fund Cayman is investing in Mangrove Master Fund. The principal business of Mangrove Fund Cayman Drawdown is investing in Mangrove Master Fund. The principal business of Mangrove Fund Cayman Partnership is investing in Mangrove Master Fund. The principal business of Mangrove Partners is serving as the investment manager of each of Mangrove Master Fund, Mangrove Fund, Mangrove Fund Cayman, Mangrove Fund Cayman Drawdown and Mangrove Fund Cayman Partnership. The principal business of Mangrove Capital is serving as the general partner of each of Mangrove Fund Cayman Drawdown and Mangrove Fund Cayman Partnership. The principal business of Mangrove Capital II is serving as the general partner of Mangrove Fund. The principal occupation of Mr. August is serving as a director of each of Mangrove Partners, Mangrove Capital and Mangrove Capital II.

(d)       No Reporting Person, nor any person listed on Schedule A , has, during the last five (5) years, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e)       No Reporting Person, nor any person listed on Schedule A , has, during the last five (5) years, been party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f)       Mr. August is a citizen of the United States of America.

Item 3 is hereby amended and restated to read as follows:

The 7,977,910 Shares directly owned by Mangrove Master Fund were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted, as set forth in Schedule B annexed hereto (“ Schedule B ”). The aggregate purchase price of the 7,977,910 Shares directly owned by Mangrove Master Fund is, in U.S. dollar terms, approximately $17,056,486, including brokerage commissions.

Items 5(a)-(c) are hereby amended and restated to read as follows:

The aggregate percentage of Shares reported owned by each person named herein is based upon 109,994,268 Shares outstanding as of October 31, 2018, which is the total number of Shares outstanding as reported in the Issuer’s Form 10-Q filed with the Securities and Exchange Commission on November 1, 2018.

Percentage: Approximately 7.3%

Percentage: Approximately 7.3%

Percentage: Approximately 7.3%

Percentage: Approximately 7.3%

Percentage: Approximately 7.3%

Percentage: Approximately 7.3%

Percentage: Approximately 7.3%

Percentage: Approximately 7.3%

Percentage: Approximately 7.3%

As of the close of business on November 14, 2018, the Reporting Persons collectively beneficially owned an aggregate of 7,977,910 Shares, constituting approximately 7.3% of the Shares outstanding.

Each of the Reporting Persons, as a member of a “group” with the other Reporting Persons for purposes of Rule 13d-5(b)(1) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), may be deemed to beneficially own the securities of the Issuer owned by the other Reporting Persons. The filing of this Schedule 13D shall not be deemed an admission that the Reporting Persons are, for purposes of Section 13(d) of the Exchange Act, the beneficial owners of any securities of the Issuer he or it does not directly own. Each of the Reporting Persons specifically disclaims beneficial ownership of the securities of the Issuer reported herein that he or it does not directly own.

Item 6 is hereby amended and restated to read as follows:

Since January 10, 2018, Mangrove Master Fund entered into a series of cash-settled total return swap agreements with each of Morgan Stanley Capital Services LLC and Barclays Bank PLC as counterparties (the “Swaps”) that establish economic exposure to an aggregate of 9,095,840 notional Shares (the “Subject Shares”), representing in the aggregate approximately 8.3% of the outstanding Shares. The Swaps provide Mangrove Master Fund with economic exposure that is comparable to the economic exposure of ownership but do not provide it with the power to vote or direct the voting of or to dispose or direct the disposition of the Subject Shares. The Reporting Persons hereby expressly disclaim beneficial ownership of the Subject Shares.

On November 15, 2018, the Reporting Persons entered into a Joint Filing Agreement pursuant to which the Reporting Persons agreed to the joint filing on behalf of each of them of statements on Schedule 13D with respect to the securities of the Issuer to the extent required by applicable law. The Joint Filing Agreement is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Item 7 is hereby amended to add the following exhibit:

SIGNATURES

After reasonable inquiry and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: November 15, 2018

SCHEDULE A

Directors of The Mangrove Partners Master Fund, Ltd. and Mangrove Partners Fund (Cayman), Ltd.

Directors of Mangrove Capital

Directors of Mangrove Capital II, Inc.

SCHEDULE B

Transactions in the Securities of the Issuer Since the Filing of Amendment No. 7 to the Schedule 13D

THE MANGROVE PARTNERS MASTER FUND, LTD.